diff --git a/integration_tests/handler/project_test.go b/integration_tests/handler/project_test.go
index e4870488..b4f47645 100644
--- a/integration_tests/handler/project_test.go
+++ b/integration_tests/handler/project_test.go
@@ -86,6 +86,7 @@ func TestCreateProject(t *testing.T) {
 		tooLongName             = strings.Repeat("亜", 33)
 		tooLongDescriptionKanji = strings.Repeat("亜", 257)
 		duration                = schema.ConvertDuration(random.Duration())
+		conflictedProject       = random.CreateProjectArgs()
 	)
 
 	t.Parallel()
@@ -179,6 +180,15 @@ func TestCreateProject(t *testing.T) {
 			},
 			httpError(t, "Bad Request: argument error"),
 		},
+		"400 project already exists": {
+			http.StatusBadRequest,
+			schema.CreateProjectRequest{
+				Name:        conflictedProject.Name,
+				Link:        &link,
+				Description: description,
+			},
+			httpError(t, "Bad Request: argument error"),
+		},
 	}
 
 	e := echo.New()
@@ -186,6 +196,7 @@ func TestCreateProject(t *testing.T) {
 	for name, tt := range tests {
 		t.Run(name, func(t *testing.T) {
 			t.Parallel()
+			_ = doRequest(t, e, http.MethodPost, e.URL(api.Project.CreateProject), &conflictedProject)
 			res := doRequest(t, e, http.MethodPost, e.URL(api.Project.CreateProject), &tt.reqBody)
 			switch want := tt.want.(type) {
 			case schema.Project:
diff --git a/internal/infrastructure/migration/current.go b/internal/infrastructure/migration/current.go
index 3b205e2e..08e562fe 100644
--- a/internal/infrastructure/migration/current.go
+++ b/internal/infrastructure/migration/current.go
@@ -9,6 +9,7 @@ import (
 func Migrations() []*gormigrate.Migration {
 	return []*gormigrate.Migration{
 		v1(),
+		v2(), // プロジェクト名とコンテスト名の重複禁止と文字数制限増加(32->128)
 	}
 }
 
diff --git a/internal/infrastructure/migration/v2.go b/internal/infrastructure/migration/v2.go
new file mode 100644
index 00000000..272bd368
--- /dev/null
+++ b/internal/infrastructure/migration/v2.go
@@ -0,0 +1,169 @@
+// Package migration migrate current struct
+package migration
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/go-gormigrate/gormigrate/v2"
+	"github.com/gofrs/uuid"
+	"github.com/traPtitech/traPortfolio/internal/infrastructure/repository/model"
+	"gorm.io/gorm"
+)
+
+// v1 unique_index:idx_room_uniqueの削除
+func v2() *gormigrate.Migration {
+	return &gormigrate.Migration{
+		ID: "2",
+		Migrate: func(db *gorm.DB) error {
+			if err := db.AutoMigrate(&v2Project{}, &v2Contest{}, &v2ContestTeam{}); err != nil {
+				return err
+			}
+
+			// プロジェクト名の重複禁止
+			{
+				projects := make([]*model.Project, 0)
+				if err := db.Find(&projects).Error; err != nil {
+					return err
+				}
+
+				projectMap := make(map[string][]uuid.UUID, len(projects))
+				for _, p := range projects {
+					projectMap[p.Name] = append(projectMap[p.Name], p.ID)
+				}
+
+				updates := make(map[uuid.UUID]string, len(projects))
+				for {
+					noDuplicate := true
+					for name, ids := range projectMap {
+						if len(ids) <= 1 {
+							continue
+						}
+						noDuplicate = false
+						for i, pid := range ids {
+							if i == 0 {
+								projectMap[name] = []uuid.UUID{pid}
+								continue
+							}
+							nameNew := fmt.Sprintf("%s (%d)", name, i)
+							updates[pid] = nameNew
+							projectMap[nameNew] = append(projectMap[nameNew], pid)
+						}
+					}
+					if noDuplicate {
+						break
+					}
+				}
+
+				for id, nameNew := range updates {
+					err := db.
+						Model(&model.Project{}).
+						Where(&model.Project{ID: id}).
+						Update("name", nameNew).
+						Error
+					if err != nil {
+						return err
+					}
+				}
+			}
+
+			// コンテスト名の重複禁止
+			{
+				contests := make([]*model.Contest, 0)
+				if err := db.Find(&contests).Error; err != nil {
+					return err
+				}
+
+				contestMap := make(map[string][]uuid.UUID, len(contests))
+				for _, c := range contests {
+					contestMap[c.Name] = append(contestMap[c.Name], c.ID)
+				}
+
+				updates := make(map[uuid.UUID]string, len(contests))
+				noDuplicate := false
+				for !noDuplicate {
+					noDuplicate = true
+					for name, ids := range contestMap {
+						if len(ids) <= 1 {
+							continue
+						}
+						noDuplicate = false
+						for i, cid := range ids {
+							if i == 0 {
+								contestMap[name] = []uuid.UUID{cid}
+								continue
+							}
+							nameNew := fmt.Sprintf("%s (%d)", name, i)
+							updates[cid] = nameNew
+							contestMap[nameNew] = append(contestMap[nameNew], cid)
+						}
+					}
+				}
+
+				for id, nameNew := range updates {
+					err := db.
+						Model(&model.Contest{}).
+						Where(&model.Contest{ID: id}).
+						Update("name", nameNew).
+						Error
+					if err != nil {
+						return err
+					}
+				}
+			}
+
+			return db.
+				Table("portfolio").
+				Error
+		},
+	}
+}
+
+type v2Project struct {
+	ID            uuid.UUID `gorm:"type:char(36);not null;primaryKey"`
+	Name          string    `gorm:"type:varchar(128)"` // 制限増加 (32->128)
+	Description   string    `gorm:"type:text"`
+	Link          string    `gorm:"type:text"`
+	SinceYear     int       `gorm:"type:smallint(4);not null"`
+	SinceSemester int       `gorm:"type:tinyint(1);not null"`
+	UntilYear     int       `gorm:"type:smallint(4);not null"`
+	UntilSemester int       `gorm:"type:tinyint(1);not null"`
+	CreatedAt     time.Time `gorm:"precision:6"`
+	UpdatedAt     time.Time `gorm:"precision:6"`
+}
+
+func (*v2Project) TableName() string {
+	return "projects"
+}
+
+type v2Contest struct {
+	ID          uuid.UUID `gorm:"type:char(36);not null;primaryKey"`
+	Name        string    `gorm:"type:varchar(128)"` // 制限増加 (32->128)
+	Description string    `gorm:"type:text"`
+	Link        string    `gorm:"type:text"`
+	Since       time.Time `gorm:"precision:6"`
+	Until       time.Time `gorm:"precision:6"`
+	CreatedAt   time.Time `gorm:"precision:6"`
+	UpdatedAt   time.Time `gorm:"precision:6"`
+}
+
+func (*v2Contest) TableName() string {
+	return "contests"
+}
+
+type v2ContestTeam struct {
+	ID          uuid.UUID `gorm:"type:char(36);not null;primaryKey"`
+	ContestID   uuid.UUID `gorm:"type:char(36);not null"`
+	Name        string    `gorm:"type:varchar(128)"` // 制限増加 (32->128)
+	Description string    `gorm:"type:text"`
+	Result      string    `gorm:"type:text"`
+	Link        string    `gorm:"type:text"`
+	CreatedAt   time.Time `gorm:"precision:6"`
+	UpdatedAt   time.Time `gorm:"precision:6"`
+
+	Contest model.Contest `gorm:"foreignKey:ContestID;constraint:OnUpdate:CASCADE,OnDelete:CASCADE"`
+}
+
+func (*v2ContestTeam) TableName() string {
+	return "contest_teams"
+}
diff --git a/internal/infrastructure/repository/contest_impl.go b/internal/infrastructure/repository/contest_impl.go
index 11af9beb..6971ce4f 100644
--- a/internal/infrastructure/repository/contest_impl.go
+++ b/internal/infrastructure/repository/contest_impl.go
@@ -2,6 +2,7 @@ package repository
 
 import (
 	"context"
+	"errors"
 
 	"github.com/gofrs/uuid"
 	"github.com/traPtitech/traPortfolio/internal/domain"
@@ -80,7 +81,19 @@ func (r *ContestRepository) CreateContest(ctx context.Context, args *repository.
 		Until:       args.Until.ValueOrZero(),
 	}
 
-	err := r.h.WithContext(ctx).Create(contest).Error
+	// 既に同名のコンテストが存在するか
+	err := r.h.
+		WithContext(ctx).
+		Where(&model.Contest{Name: contest.Name}).
+		First(&model.Contest{}).
+		Error
+	if err == nil {
+		return nil, repository.ErrAlreadyExists
+	} else if !errors.Is(err, repository.ErrNotFound) {
+		return nil, err
+	}
+
+	err = r.h.WithContext(ctx).Create(contest).Error
 	if err != nil {
 		return nil, err
 	}
diff --git a/internal/infrastructure/repository/contest_test.go b/internal/infrastructure/repository/contest_test.go
index 571cb467..d1285e65 100644
--- a/internal/infrastructure/repository/contest_test.go
+++ b/internal/infrastructure/repository/contest_test.go
@@ -62,7 +62,37 @@ func Test_GetContest(t *testing.T) {
 	})
 }
 
-func Test_CreateContest(t *testing.T) {}
+func Test_CreateContest(t *testing.T) {
+	t.Parallel()
+
+	db := SetupTestGormDB(t)
+	portalAPI := mock_external.NewMockPortalAPI(gomock.NewController(t))
+	repo := NewContestRepository(db, portalAPI)
+
+	t.Run("create a contest", func(t *testing.T) {
+		ctx := context.Background()
+		args := random.CreateContestArgs()
+		contest, err := repo.CreateContest(ctx, args)
+		assert.NoError(t, err)
+
+		gotContest, err := repo.GetContest(ctx, contest.ID)
+		assert.NoError(t, err)
+		assert.Equal(t, contest, gotContest)
+	})
+
+	t.Run("create contests which name duplicated", func(t *testing.T) {
+		ctx := context.Background()
+		arg1 := random.CreateContestArgs()
+		arg2 := random.CreateContestArgs()
+		arg2.Name = arg1.Name
+
+		_, err := repo.CreateContest(ctx, arg1)
+		assert.NoError(t, err)
+
+		_, err = repo.CreateContest(ctx, arg2)
+		assert.Error(t, err)
+	})
+}
 
 func Test_UpdateContest(t *testing.T) {
 	t.Parallel()
diff --git a/internal/infrastructure/repository/model/contests.go b/internal/infrastructure/repository/model/contests.go
index 2925d63b..2631e85e 100644
--- a/internal/infrastructure/repository/model/contests.go
+++ b/internal/infrastructure/repository/model/contests.go
@@ -8,7 +8,7 @@ import (
 
 type Contest struct {
 	ID          uuid.UUID `gorm:"type:char(36);not null;primaryKey"`
-	Name        string    `gorm:"type:varchar(32)"`
+	Name        string    `gorm:"type:varchar(128)"`
 	Description string    `gorm:"type:text"`
 	Link        string    `gorm:"type:text"`
 	Since       time.Time `gorm:"precision:6"`
@@ -24,7 +24,7 @@ func (*Contest) TableName() string {
 type ContestTeam struct {
 	ID          uuid.UUID `gorm:"type:char(36);not null;primaryKey"`
 	ContestID   uuid.UUID `gorm:"type:char(36);not null"`
-	Name        string    `gorm:"type:varchar(32)"`
+	Name        string    `gorm:"type:varchar(128)"`
 	Description string    `gorm:"type:text"`
 	Result      string    `gorm:"type:text"`
 	Link        string    `gorm:"type:text"`
diff --git a/internal/infrastructure/repository/model/project.go b/internal/infrastructure/repository/model/project.go
index 97eb506f..9222ac08 100644
--- a/internal/infrastructure/repository/model/project.go
+++ b/internal/infrastructure/repository/model/project.go
@@ -8,7 +8,7 @@ import (
 
 type Project struct {
 	ID            uuid.UUID `gorm:"type:char(36);not null;primaryKey"`
-	Name          string    `gorm:"type:varchar(32)"`
+	Name          string    `gorm:"type:varchar(128)"`
 	Description   string    `gorm:"type:text"`
 	Link          string    `gorm:"type:text"`
 	SinceYear     int       `gorm:"type:smallint(4);not null"`
diff --git a/internal/infrastructure/repository/project_impl.go b/internal/infrastructure/repository/project_impl.go
index bbacd71a..abd1ae8f 100644
--- a/internal/infrastructure/repository/project_impl.go
+++ b/internal/infrastructure/repository/project_impl.go
@@ -2,6 +2,7 @@ package repository
 
 import (
 	"context"
+	"errors"
 	"fmt"
 
 	"github.com/gofrs/uuid"
@@ -106,7 +107,19 @@ func (r *ProjectRepository) CreateProject(ctx context.Context, args *repository.
 	}
 	p.Link = args.Link.ValueOr(p.Link)
 
-	err := r.h.WithContext(ctx).Create(&p).Error
+	// 既に同名のプロジェクトが存在するか
+	err := r.h.
+		WithContext(ctx).
+		Where(&model.Project{Name: p.Name}).
+		First(&model.Project{}).
+		Error
+	if err == nil {
+		return nil, repository.ErrAlreadyExists
+	} else if !errors.Is(err, repository.ErrNotFound) {
+		return nil, err
+	}
+
+	err = r.h.WithContext(ctx).Create(&p).Error
 	if err != nil {
 		return nil, err
 	}
diff --git a/internal/infrastructure/repository/project_test.go b/internal/infrastructure/repository/project_test.go
index d7534312..64e95179 100644
--- a/internal/infrastructure/repository/project_test.go
+++ b/internal/infrastructure/repository/project_test.go
@@ -60,8 +60,53 @@ func TestProjectRepository_GetProject(t *testing.T) {
 	}
 }
 
-// func TestProjectRepository_CreateProject(t *testing.T) {
-// }
+func TestProjectRepository_CreateProject(t *testing.T) {
+	t.Parallel()
+
+	db := SetupTestGormDB(t)
+	repo := NewProjectRepository(db, mock_external_e2e.NewMockPortalAPI())
+
+	t.Run("create project success", func(t *testing.T) {
+		ctx := context.Background()
+		arg := random.CreateProjectArgs()
+
+		project, err := repo.CreateProject(ctx, arg)
+		assert.NoError(t, err)
+
+		got, err := repo.GetProject(ctx, project.ID)
+		assert.NoError(t, err)
+
+		opts := []cmp.Option{
+			cmpopts.EquateEmpty(),
+			cmp.AllowUnexported(optional.Of[domain.YearWithSemester]{}),
+		}
+		if diff := cmp.Diff(project, got, opts...); diff != "" {
+			t.Error(diff)
+		}
+	})
+
+	t.Run("create project with invalid args", func(t *testing.T) {
+		ctx := context.Background()
+		arg := random.CreateProjectArgs()
+		arg.Name = ""
+
+		_, err := repo.CreateProject(ctx, arg)
+		assert.Error(t, err)
+	})
+
+	t.Run("create projects which name duplicated", func(t *testing.T) {
+		ctx := context.Background()
+		arg1 := random.CreateProjectArgs()
+		arg2 := random.CreateProjectArgs()
+		arg2.Name = arg1.Name
+
+		_, err := repo.CreateProject(ctx, arg1)
+		assert.NoError(t, err)
+
+		_, err = repo.CreateProject(ctx, arg2)
+		assert.Error(t, err)
+	})
+}
 
 func TestProjectRepository_UpdateProject(t *testing.T) {
 	t.Parallel()
diff --git a/internal/pkgs/random/repository.go b/internal/pkgs/random/repository.go
index d345cf6b..a355d09f 100644
--- a/internal/pkgs/random/repository.go
+++ b/internal/pkgs/random/repository.go
@@ -64,6 +64,19 @@ func OptUpdateContestTeamArgs() *repository.UpdateContestTeamArgs {
 	return &a
 }
 
+// CreateProjectArgs 全てのフィールドがvalidなCreateProjectArgsを生成します
+func CreateProjectArgs() *repository.CreateProjectArgs {
+	return &repository.CreateProjectArgs{
+		Name:          AlphaNumeric(),
+		Description:   AlphaNumeric(),
+		Link:          Optional(RandURLString()),
+		SinceYear:     2100,
+		SinceSemester: 0,
+		UntilYear:     2100,
+		UntilSemester: 1,
+	}
+}
+
 // UpdateProjectArgs 全てのフィールドがvalidなUpdateProjectArgsを生成します
 func UpdateProjectArgs() *repository.UpdateProjectArgs {
 	a := repository.UpdateProjectArgs{