diff --git a/db/seeds.rb b/db/seeds.rb
index b66aa3e..c669b0e 100644
--- a/db/seeds.rb
+++ b/db/seeds.rb
@@ -2,8 +2,295 @@
 
 # This file should contain all the record creation needed to seed the database with its default values.
 # The data can then be loaded with the rails db:seed command (or created alongside the database with db:setup).
-#
-# Examples:
-#
-#   movies = Movie.create([{ name: 'Star Wars' }, { name: 'Lord of the Rings' }])
-#   Character.create(name: 'Luke', movie: movies.first)
+
+puts "🌱 Seeding database..."
+
+# Create admin user
+admin_user = User.create!(
+  name: "admin",
+  email: "admin@example.com",
+  password: "password",
+  password_confirmation: "password",
+  role: "admin",
+  confirmed_at: Time.current
+)
+puts "✅ Created admin user: #{admin_user.name}"
+
+# Create sample users
+users = []
+5.times do |i|
+  user = User.create!(
+    name: "user#{i + 1}",
+    email: "user#{i + 1}@example.com",
+    password: "password",
+    password_confirmation: "password",
+    role: "member",
+    atcoder_id: "user#{i + 1}",
+    atcoder_rating: rand(400..2800),
+    confirmed_at: Time.current
+  )
+  users << user
+  puts "✅ Created user: #{user.name}"
+end
+
+# Create writer user
+writer_user = User.create!(
+  name: "writer",
+  email: "writer@example.com",
+  password: "password",
+  password_confirmation: "password",
+  role: "writer",
+  confirmed_at: Time.current
+)
+puts "✅ Created writer user: #{writer_user.name}"
+
+# Create sample contests
+past_contest = Contest.create!(
+  slug: "sample-contest-2024",
+  name: "Sample Contest 2024",
+  description: "これはサンプルコンテストです。",
+  kind: "normal",
+  allow_open_registration: true,
+  allow_team_registration: false,
+  standings_mode: 1,
+  penalty_time: 5,
+  start_at: 1.month.ago,
+  end_at: 1.month.ago + 3.hours,
+  permanent: false,
+  official_mode: true
+)
+puts "✅ Created past contest: #{past_contest.name}"
+
+upcoming_contest = Contest.create!(
+  slug: "upcoming-contest",
+  name: "Upcoming Contest",
+  description: "これから開催されるコンテストです。",
+  kind: "normal",
+  allow_open_registration: true,
+  allow_team_registration: true,
+  standings_mode: 1,
+  penalty_time: 5,
+  start_at: 1.week.from_now,
+  end_at: 1.week.from_now + 3.hours,
+  permanent: false,
+  official_mode: true
+)
+puts "✅ Created upcoming contest: #{upcoming_contest.name}"
+
+practice_contest = Contest.create!(
+  slug: "practice",
+  name: "Practice Contest",
+  description: "練習用のコンテストです。いつでも参加できます。",
+  kind: "normal",
+  allow_open_registration: true,
+  allow_team_registration: false,
+  standings_mode: 1,
+  penalty_time: 0,
+  start_at: 1.year.ago,
+  end_at: nil,
+  permanent: true,
+  official_mode: false
+)
+puts "✅ Created practice contest: #{practice_contest.name}"
+
+# Create sample problems
+problem_a = Problem.create!(
+  slug: "sample-a",
+  name: "A + B Problem",
+  contest_id: past_contest.id,
+  writer_user_id: writer_user.id,
+  position: "A",
+  uuid: SecureRandom.uuid,
+  difficulty: "beginner",
+  execution_time_limit: 2000,
+  submission_limit_1: 5,
+  submission_limit_2: 60,
+  statement: "2つの整数 A, B が与えられます。A + B を出力してください。",
+  constraints: "1 ≤ A, B ≤ 1000",
+  input_format: "A B",
+  output_format: "A + B の値"
+)
+puts "✅ Created problem: #{problem_a.name}"
+
+problem_b = Problem.create!(
+  slug: "sample-b",
+  name: "Factorial",
+  contest_id: past_contest.id,
+  writer_user_id: writer_user.id,
+  position: "B",
+  uuid: SecureRandom.uuid,
+  difficulty: "easy",
+  execution_time_limit: 2000,
+  submission_limit_1: 5,
+  submission_limit_2: 60,
+  statement: "正の整数 N が与えられます。N! (N の階乗) を出力してください。",
+  constraints: "1 ≤ N ≤ 10",
+  input_format: "N",
+  output_format: "N! の値"
+)
+puts "✅ Created problem: #{problem_b.name}"
+
+practice_problem = Problem.create!(
+  slug: "hello-world",
+  name: "Hello World",
+  contest_id: practice_contest.id,
+  writer_user_id: writer_user.id,
+  position: "A",
+  uuid: SecureRandom.uuid,
+  difficulty: "beginner",
+  execution_time_limit: 1000,
+  submission_limit_1: 10,
+  submission_limit_2: 100,
+  statement: "\"Hello World\" を出力してください。",
+  constraints: "特になし",
+  input_format: "入力はありません。",
+  output_format: "Hello World"
+)
+puts "✅ Created practice problem: #{practice_problem.name}"
+
+# Create testcases for problems
+# A + B Problem testcases
+testcase_a1 = Testcase.create!(
+  problem_id: problem_a.id,
+  name: "sample_01",
+  input: "1 2",
+  output: "3",
+  explanation: "1 + 2 = 3"
+)
+
+testcase_a2 = Testcase.create!(
+  problem_id: problem_a.id,
+  name: "sample_02",
+  input: "100 200",
+  output: "300",
+  explanation: "100 + 200 = 300"
+)
+
+# Factorial testcases
+testcase_b1 = Testcase.create!(
+  problem_id: problem_b.id,
+  name: "sample_01",
+  input: "3",
+  output: "6",
+  explanation: "3! = 3 × 2 × 1 = 6"
+)
+
+testcase_b2 = Testcase.create!(
+  problem_id: problem_b.id,
+  name: "sample_02",
+  input: "5",
+  output: "120",
+  explanation: "5! = 5 × 4 × 3 × 2 × 1 = 120"
+)
+
+# Hello World testcase
+testcase_hello = Testcase.create!(
+  problem_id: practice_problem.id,
+  name: "sample_01",
+  input: "",
+  output: "Hello World",
+  explanation: "Hello World を出力する"
+)
+
+puts "✅ Created testcases"
+
+# Create testcase sets
+testcase_set_a = TestcaseSet.create!(
+  problem_id: problem_a.id,
+  name: "All",
+  points: 100,
+  aggregate_type: 0,
+  is_sample: true
+)
+
+testcase_set_b = TestcaseSet.create!(
+  problem_id: problem_b.id,
+  name: "All", 
+  points: 100,
+  aggregate_type: 0,
+  is_sample: true
+)
+
+testcase_set_hello = TestcaseSet.create!(
+  problem_id: practice_problem.id,
+  name: "All",
+  points: 100,
+  aggregate_type: 0,
+  is_sample: true
+)
+
+# Associate testcases with testcase sets
+TestcaseTestcaseSet.create!(testcase_id: testcase_a1.id, testcase_set_id: testcase_set_a.id)
+TestcaseTestcaseSet.create!(testcase_id: testcase_a2.id, testcase_set_id: testcase_set_a.id)
+TestcaseTestcaseSet.create!(testcase_id: testcase_b1.id, testcase_set_id: testcase_set_b.id)
+TestcaseTestcaseSet.create!(testcase_id: testcase_b2.id, testcase_set_id: testcase_set_b.id)
+TestcaseTestcaseSet.create!(testcase_id: testcase_hello.id, testcase_set_id: testcase_set_hello.id)
+
+puts "✅ Created testcase sets and associations"
+
+# Create registrations for past contest
+users.each do |user|
+  Registration.create!(
+    user_id: user.id,
+    contest_id: past_contest.id,
+    open_registration: true
+  )
+end
+puts "✅ Created registrations for past contest"
+
+# Create some sample submissions
+users.first(3).each_with_index do |user, index|
+  Submission.create!(
+    user_id: user.id,
+    problem_id: problem_a.id,
+    path: "submissions/#{user.id}/#{problem_a.id}/main.cpp",
+    status: index == 0 ? "AC" : ["WA", "TLE", "RE"].sample,
+    point: index == 0 ? 100 : 0,
+    execution_time: rand(100..1500),
+    execution_memory: rand(1000..50000),
+    lang: "cpp",
+    public: true
+  )
+end
+puts "✅ Created sample submissions"
+
+# Create contest admins
+ContestAdmin.create!(
+  contest_id: past_contest.id,
+  user_id: admin_user.id
+)
+
+ContestAdmin.create!(
+  contest_id: upcoming_contest.id,
+  user_id: admin_user.id
+)
+
+ContestAdmin.create!(
+  contest_id: practice_contest.id,
+  user_id: admin_user.id
+)
+puts "✅ Created contest admins"
+
+# Create sample posts
+Post.create!(
+  title: "サイトオープンのお知らせ",
+  content: "競技プログラミングオンラインジャッジサイトがオープンしました！\n\nこのサイトでは以下のことができます：\n- プログラミングコンテストに参加\n- 問題の練習\n- 他の参加者との交流\n\nぜひご利用ください！",
+  public_status: "public"
+)
+
+Post.create!(
+  title: "初回コンテスト開催のお知らせ",
+  content: "記念すべき第1回コンテストを開催します！\n\n日時：来週の土曜日 20:00-23:00\n難易度：初心者〜中級者向け\n\n皆様のご参加をお待ちしております。",
+  public_status: "public"
+)
+puts "✅ Created sample posts"
+
+puts "🎉 Database seeded successfully!"
+puts ""
+puts "📊 Summary:"
+puts "- Users: #{User.count}"
+puts "- Contests: #{Contest.count}"
+puts "- Problems: #{Problem.count}"
+puts "- Testcases: #{Testcase.count}"
+puts "- Submissions: #{Submission.count}"
+puts "- Posts: #{Post.count}"
\ No newline at end of file