diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index 1bdc29d81..3186fc47b 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -473,7 +473,7 @@ module ApplicationHelper
         end
         classes = (ancestors.empty? ? 'root' : 'child')
         classes += ' archived' if project.archived?
-        s << "<li class='#{classes}'><div class='#{classes}'>"
+        s << "<li class='#{classes}' data-project-id='#{project.id}'><div class='#{classes}'>"
         s << h(block ? capture(project, &block) : project.name)
         s << "</div>\n"
         ancestors << project
diff --git a/app/javascript/controllers/project_selector_controller.js b/app/javascript/controllers/project_selector_controller.js
new file mode 100644
index 000000000..2c3158c0a
--- /dev/null
+++ b/app/javascript/controllers/project_selector_controller.js
@@ -0,0 +1,20 @@
+import { Controller } from "@hotwired/stimulus";
+
+export default class extends Controller {
+  toggleChildProjects(event) {
+    const checkbox = event.target;
+    if (checkbox.type !== 'checkbox') return;
+
+    const listItem = checkbox.closest('li');
+    if (!listItem) return;
+
+    const childList = listItem.querySelector('ul.projects');
+    if (!childList) return;
+
+    const childCheckboxes = childList.querySelectorAll('input[type="checkbox"]');
+
+    childCheckboxes.forEach(child => {
+      child.checked = checkbox.checked;
+    });
+  }
+}
diff --git a/app/views/custom_fields/_visibility_by_project_selector.html.erb b/app/views/custom_fields/_visibility_by_project_selector.html.erb
index 25fd4978b..6f107fe61 100644
--- a/app/views/custom_fields/_visibility_by_project_selector.html.erb
+++ b/app/views/custom_fields/_visibility_by_project_selector.html.erb
@@ -1,11 +1,11 @@
 <fieldset class="box"><legend><%= toggle_checkboxes_link("#custom_field_project_ids input[type=checkbox]:enabled") %><%= l(:label_project_plural) %></legend>
   <p><%= f.check_box :is_for_all, :data => {:disables => '#custom_field_project_ids input'} %></p>
 
-  <div id="custom_field_project_ids">
+  <div id="custom_field_project_ids" data-controller="project-selector">
     <% project_ids = @custom_field.project_ids.to_a %>
     <%= render_project_nested_lists(Project.all) do |p|
-      content_tag('label', check_box_tag('custom_field[project_ids][]', p.id, project_ids.include?(p.id), :id => nil) + ' ' + p.to_s)
+      content_tag('label', check_box_tag('custom_field[project_ids][]', p.id, project_ids.include?(p.id), :id => nil, :data => {:action => 'change->project-selector#toggleChildProjects'}) + ' ' + p.to_s)
     end %>
     <%= hidden_field_tag('custom_field[project_ids][]', '', :id => nil) %>
   </div>
-</fieldset>
+</fieldset>
\ No newline at end of file
diff --git a/test/system/custom_field_project_selector_test.rb b/test/system/custom_field_project_selector_test.rb
new file mode 100644
index 000000000..91180e15f
--- /dev/null
+++ b/test/system/custom_field_project_selector_test.rb
@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+
+require_relative '../application_system_test_case'
+
+class CustomFieldProjectSelectorTest < ApplicationSystemTestCase
+  setup do
+    @parent = Project.generate!(name: 'Parent Project')
+    @child1 = Project.generate!(name: 'Child Project 1', parent_id: @parent.id)
+    @child2 = Project.generate!(name: 'Child Project 2', parent_id: @parent.id)
+    @grandchild = Project.generate!(name: 'Grandchild Project', parent_id: @child1.id)
+  end
+
+  def test_checking_parent_project_should_check_child_projects
+    log_user('admin', 'admin')
+
+    custom_field = IssueCustomField.generate!(
+      field_format: 'string',
+      name: 'Test Field',
+      is_for_all: false
+    )
+
+    visit "/custom_fields/#{custom_field.id}/edit"
+
+    within '#custom_field_project_ids' do
+      parent_checkbox = find("input[value='#{@parent.id}']")
+      parent_checkbox.click
+
+      child1_checkbox = find("input[value='#{@child1.id}']")
+      child2_checkbox = find("input[value='#{@child2.id}']")
+
+      assert child1_checkbox.checked?, 'Child project 1 should be checked'
+      assert child2_checkbox.checked?, 'Child project 2 should be checked'
+    end
+  end
+
+  def test_unchecking_parent_project_should_uncheck_child_projects
+    log_user('admin', 'admin')
+
+    custom_field = IssueCustomField.generate!(
+      field_format: 'string',
+      name: 'Test Field',
+      is_for_all: false,
+      project_ids: [@parent.id, @child1.id, @child2.id]
+    )
+
+    visit "/custom_fields/#{custom_field.id}/edit"
+
+    within '#custom_field_project_ids' do
+      parent_checkbox = find("input[value='#{@parent.id}']")
+      child1_checkbox = find("input[value='#{@child1.id}']")
+      child2_checkbox = find("input[value='#{@child2.id}']")
+
+      assert parent_checkbox.checked?, 'Parent should be checked initially'
+      assert child1_checkbox.checked?, 'Child 1 should be checked initially'
+      assert child2_checkbox.checked?, 'Child 2 should be checked initially'
+
+      parent_checkbox.click
+
+      assert !child1_checkbox.checked?, 'Child project 1 should be unchecked'
+      assert !child2_checkbox.checked?, 'Child project 2 should be unchecked'
+    end
+  end
+
+  def test_grandchild_projects_are_also_synced
+    log_user('admin', 'admin')
+
+    custom_field = IssueCustomField.generate!(
+      field_format: 'string',
+      name: 'Test Field',
+      is_for_all: false
+    )
+
+    visit "/custom_fields/#{custom_field.id}/edit"
+
+    within '#custom_field_project_ids' do
+      parent_checkbox = find("input[value='#{@parent.id}']")
+      parent_checkbox.click
+
+      grandchild_checkbox = find("input[value='#{@grandchild.id}']")
+      assert grandchild_checkbox.checked?, 'Grandchild project should be checked'
+    end
+  end
+end
\ No newline at end of file