diff --git a/app/controllers/shopkeeper_auth/registrations_controller.rb b/app/controllers/shopkeeper_auth/registrations_controller.rb
index b25469c..fd5d44e 100644
--- a/app/controllers/shopkeeper_auth/registrations_controller.rb
+++ b/app/controllers/shopkeeper_auth/registrations_controller.rb
@@ -1,4 +1,10 @@
 class ShopkeeperAuth::RegistrationsController < DeviseTokenAuth::RegistrationsController
+  rate_limit to: 10, within: 3.minutes, only: :create,
+    with: -> {
+      render json: {code: 429, error_message: I18n.t("errors.messages.too_many_signups")},
+        status: :too_many_requests
+    }
+
   before_action :set_confirm_success_url, only: %i[create]
   before_action :configure_permitted_parameters
 
diff --git a/config/environments/test.rb b/config/environments/test.rb
index 411227e..30e57b4 100644
--- a/config/environments/test.rb
+++ b/config/environments/test.rb
@@ -22,7 +22,9 @@
 
   # Show full error reports and disable caching.
   config.consider_all_requests_local = true
-  config.cache_store = :null_store
+  # Use memory store so ActionController::RateLimiting can persist counters
+  # between requests within a test; null_store would no-op the increments.
+  config.cache_store = :memory_store
 
   # Render exception templates for rescuable exceptions and raise for other exceptions.
   config.action_dispatch.show_exceptions = :rescuable
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 626b6d1..c4dcd6e 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -142,3 +142,4 @@ en:
       limit_count_shop: "You can create up to %{limit_count} shops across all organizations."
       limit_count_accounts_shopkeeper: "Organization members can be created up to %{limit_count}. Please contact the organization admin user or owner."
       limit_count_item_tag: "You can create up to %{limit_count} item tags."
+      too_many_signups: "Too many sign-up attempts. Please try again later."
diff --git a/test/integration/sign_up_throttle_test.rb b/test/integration/sign_up_throttle_test.rb
new file mode 100644
index 0000000..f440de1
--- /dev/null
+++ b/test/integration/sign_up_throttle_test.rb
@@ -0,0 +1,29 @@
+require "test_helper"
+
+class SignUpThrottleTest < ActionDispatch::IntegrationTest
+  def post_sign_up(email)
+    post shopkeeper_registration_url,
+      params: {
+        name: "Throttle Test",
+        email: email,
+        password: "password",
+        password_confirmation: "password",
+        time_zone: "Tokyo",
+        current_platform: "ios"
+      },
+      as: :json
+  end
+
+  test "the eleventh sign-up from the same IP within the window is rate-limited" do
+    10.times do |i|
+      post_sign_up("throttle#{i}@example.com")
+      assert_not_equal 429, response.status, "request #{i + 1} should not be throttled"
+    end
+
+    post_sign_up("throttle10@example.com")
+
+    assert_response :too_many_requests
+    assert_equal 429, response.parsed_body["code"]
+    assert_equal I18n.t("errors.messages.too_many_signups"), response.parsed_body["error_message"]
+  end
+end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 59401c1..d44ecea 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -14,6 +14,7 @@ module ActiveSupport
   class TestCase
     setup do
       Dir[Rails.root.join("db", "fixtures", "test", "*.rb")].sort.each { |s| load s }
+      Rails.cache.clear
     end
 
     # Run tests in parallel with specified workers