diff --git a/web/app/components/base/theme-selector.tsx b/web/app/components/base/theme-selector.tsx
new file mode 100644
index 0000000000..8dfe1d2602
--- /dev/null
+++ b/web/app/components/base/theme-selector.tsx
@@ -0,0 +1,97 @@
+'use client'
+
+import { useState } from 'react'
+import {
+  RiCheckLine,
+  RiComputerLine,
+  RiMoonLine,
+  RiSunLine,
+} from '@remixicon/react'
+import { useTranslation } from 'react-i18next'
+import { useTheme } from 'next-themes'
+import ActionButton from '@/app/components/base/action-button'
+import {
+  PortalToFollowElem,
+  PortalToFollowElemContent,
+  PortalToFollowElemTrigger,
+} from '@/app/components/base/portal-to-follow-elem'
+
+export type Theme = 'light' | 'dark' | 'system'
+
+export default function ThemeSelector() {
+  const { t } = useTranslation()
+  const { theme, setTheme } = useTheme()
+  const [open, setOpen] = useState(false)
+
+  const handleThemeChange = (newTheme: Theme) => {
+    setTheme(newTheme)
+    setOpen(false)
+  }
+
+  const getCurrentIcon = () => {
+    switch (theme) {
+      case 'light': return <RiSunLine className='h-4 w-4 text-text-tertiary' />
+      case 'dark': return <RiMoonLine className='h-4 w-4 text-text-tertiary' />
+      default: return <RiComputerLine className='h-4 w-4 text-text-tertiary' />
+    }
+  }
+
+  return (
+    <PortalToFollowElem
+      open={open}
+      onOpenChange={setOpen}
+      placement='bottom-end'
+      offset={{ mainAxis: 6 }}
+    >
+      <PortalToFollowElemTrigger
+        onClick={() => setOpen(!open)}
+      >
+        <ActionButton
+          className={`h-8 w-8 p-[6px] ${open && 'bg-state-base-hover'}`}
+        >
+          {getCurrentIcon()}
+        </ActionButton>
+      </PortalToFollowElemTrigger>
+      <PortalToFollowElemContent className='z-[1000]'>
+        <div className='flex w-[144px] flex-col items-start rounded-xl border-[0.5px] border-components-panel-border bg-components-panel-bg-blur p-1 shadow-lg'>
+          <button
+            className='flex w-full items-center gap-1 rounded-lg px-2 py-1.5 text-text-secondary hover:bg-state-base-hover'
+            onClick={() => handleThemeChange('light')}
+          >
+            <RiSunLine className='h-4 w-4 text-text-tertiary' />
+            <div className='flex grow items-center justify-start px-1'>
+              <span className='system-md-regular'>{t('common.theme.light')}</span>
+            </div>
+            {theme === 'light' && <div className='flex h-4 w-4 shrink-0 items-center justify-center'>
+              <RiCheckLine className='h-4 w-4 text-text-accent' />
+            </div>}
+          </button>
+          <button
+            className='flex w-full items-center gap-1 rounded-lg px-2 py-1.5 text-text-secondary hover:bg-state-base-hover'
+            onClick={() => handleThemeChange('dark')}
+          >
+            <RiMoonLine className='h-4 w-4 text-text-tertiary' />
+            <div className='flex grow items-center justify-start px-1'>
+              <span className='system-md-regular'>{t('common.theme.dark')}</span>
+            </div>
+            {theme === 'dark' && <div className='flex h-4 w-4 shrink-0 items-center justify-center'>
+              <RiCheckLine className='h-4 w-4 text-text-accent' />
+            </div>}
+          </button>
+          <button
+            className='flex w-full items-center gap-1 rounded-lg px-2 py-1.5 text-text-secondary hover:bg-state-base-hover'
+            onClick={() => handleThemeChange('system')}
+          >
+            <RiComputerLine className='h-4 w-4 text-text-tertiary' />
+            <div className='flex grow items-center justify-start px-1'>
+              <span className='system-md-regular'>{t('common.theme.auto')}</span>
+            </div>
+            {theme === 'system' && <div className='flex h-4 w-4 shrink-0 items-center justify-center'>
+              <RiCheckLine className='h-4 w-4 text-text-accent' />
+            </div>}
+          </button>
+        </div>
+      </PortalToFollowElemContent>
+    </PortalToFollowElem>
+  )
+}
diff --git a/web/app/components/base/theme-switcher.tsx b/web/app/components/base/theme-switcher.tsx
new file mode 100644
index 0000000000..902d064a66
--- /dev/null
+++ b/web/app/components/base/theme-switcher.tsx
@@ -0,0 +1,58 @@
+'use client'
+import {
+  RiComputerLine,
+  RiMoonLine,
+  RiSunLine,
+} from '@remixicon/react'
+import { useTheme } from 'next-themes'
+import cn from '@/utils/classnames'
+
+export type Theme = 'light' | 'dark' | 'system'
+
+export default function ThemeSwitcher() {
+  const { theme, setTheme } = useTheme()
+
+  const handleThemeChange = (newTheme: Theme) => {
+    setTheme(newTheme)
+  }
+
+  return (
+    <div className='flex items-center rounded-[10px] bg-components-segmented-control-bg-normal p-0.5'>
+      <div
+        className={cn(
+          'rounded-lg px-2 py-1 text-text-tertiary hover:bg-state-base-hover hover:text-text-secondary',
+          theme === 'system' && 'bg-components-segmented-control-item-active-bg text-text-accent-light-mode-only shadow-sm hover:bg-components-segmented-control-item-active-bg hover:text-text-accent-light-mode-only',
+        )}
+        onClick={() => handleThemeChange('system')}
+      >
+        <div className='p-0.5'>
+          <RiComputerLine className='h-4 w-4' />
+        </div>
+      </div>
+      <div className={cn('h-[14px] w-px bg-transparent', theme === 'dark' && 'bg-divider-regular')}></div>
+      <div
+        className={cn(
+          'rounded-lg px-2 py-1 text-text-tertiary hover:bg-state-base-hover hover:text-text-secondary',
+          theme === 'light' && 'bg-components-segmented-control-item-active-bg text-text-accent-light-mode-only shadow-sm hover:bg-components-segmented-control-item-active-bg hover:text-text-accent-light-mode-only',
+        )}
+        onClick={() => handleThemeChange('light')}
+      >
+        <div className='p-0.5'>
+          <RiSunLine className='h-4 w-4' />
+        </div>
+      </div>
+      <div className={cn('h-[14px] w-px bg-transparent', theme === 'system' && 'bg-divider-regular')}></div>
+      <div
+        className={cn(
+          'rounded-lg px-2 py-1 text-text-tertiary hover:bg-state-base-hover hover:text-text-secondary',
+          theme === 'dark' && 'bg-components-segmented-control-item-active-bg text-text-accent-light-mode-only shadow-sm hover:bg-components-segmented-control-item-active-bg hover:text-text-accent-light-mode-only',
+        )}
+        onClick={() => handleThemeChange('dark')}
+      >
+        <div className='p-0.5'>
+          <RiMoonLine className='h-4 w-4' />
+        </div>
+      </div>
+    </div>
+  )
+}
diff --git a/web/app/components/header/account-dropdown/index.tsx b/web/app/components/header/account-dropdown/index.tsx
index 66b61d7ec1..88bee4dd51 100644
--- a/web/app/components/header/account-dropdown/index.tsx
+++ b/web/app/components/header/account-dropdown/index.tsx
@@ -14,6 +14,7 @@ import {
   RiMap2Line,
   RiSettings3Line,
   RiStarLine,
+  RiTShirt2Line,
 } from '@remixicon/react'
 import Link from 'next/link'
 import { Menu, MenuButton, MenuItem, MenuItems, Transition } from '@headlessui/react'
@@ -25,6 +26,7 @@ import Compliance from './compliance'
 import PremiumBadge from '@/app/components/base/premium-badge'
 import I18n from '@/context/i18n'
 import Avatar from '@/app/components/base/avatar'
+import ThemeSwitcher from '@/app/components/base/theme-switcher'
 import { logout } from '@/service/common'
 import AppContext, { useAppContext } from '@/context/app-context'
 import { useProviderContext } from '@/context/provider-context'
@@ -83,8 +85,8 @@ export default function AppSelector() {
                 <MenuItems
                   className="
                     absolute right-0 mt-1.5 w-60 max-w-80
-                    origin-top-right divide-y divide-divider-subtle rounded-xl bg-components-panel-bg-blur
-                    shadow-lg focus:outline-none
+                    origin-top-right divide-y divide-divider-subtle rounded-xl bg-components-panel-bg-blur shadow-lg
+                    backdrop-blur-sm focus:outline-none
                   "
                 >
                   <MenuItem disabled>
@@ -189,6 +191,15 @@ export default function AppSelector() {
                       )
                     }
                   </div>
+                  <MenuItem disabled>
+                    <div className='p-1'>
+                      <div className={cn(itemClassName, 'hover:bg-transparent')}>
+                        <RiTShirt2Line className='size-4 shrink-0 text-text-tertiary' />
+                        <div className='system-md-regular grow px-1 text-text-secondary'>{t('common.theme.theme')}</div>
+                        <ThemeSwitcher/>
+                      </div>
+                    </div>
+                  </MenuItem>
                   <MenuItem>
                     <div className='p-1' onClick={() => handleLogout()}>
                       <div
diff --git a/web/app/components/share/text-generation/menu-dropdown.tsx b/web/app/components/share/text-generation/menu-dropdown.tsx
index 91605f6a9a..d038b94c1a 100644
--- a/web/app/components/share/text-generation/menu-dropdown.tsx
+++ b/web/app/components/share/text-generation/menu-dropdown.tsx
@@ -12,6 +12,8 @@ import {
   PortalToFollowElemContent,
   PortalToFollowElemTrigger,
 } from '@/app/components/base/portal-to-follow-elem'
+import Divider from '@/app/components/base/divider'
+import ThemeSwitcher from '@/app/components/base/theme-switcher'
 import InfoModal from './info-modal'
 import type { SiteInfo } from '@/models/share'
 import cn from '@/utils/classnames'
@@ -59,6 +61,13 @@ const MenuDropdown: FC<Props> = ({
         </PortalToFollowElemTrigger>
         <PortalToFollowElemContent className='z-50'>
           <div className='w-[224px] rounded-xl border-[0.5px] border-components-panel-border bg-components-panel-bg-blur shadow-lg backdrop-blur-sm'>
+            <div className='p-1'>
+              <div className={cn('system-md-regular flex cursor-pointer items-center rounded-lg py-1.5 pl-3 pr-2 text-text-secondary')}>
+                <div className='grow'>{t('common.theme.theme')}</div>
+                <ThemeSwitcher/>
+              </div>
+            </div>
+            <Divider type='horizontal' className='my-0' />
             <div className='p-1'>
               {data?.privacy_policy && (
                 <a href={data.privacy_policy} target='_blank' className='system-md-regular flex cursor-pointer items-center rounded-lg px-3 py-1.5 text-text-secondary hover:bg-state-base-hover'>
diff --git a/web/app/layout.tsx b/web/app/layout.tsx
index 6b5618f217..2143c4b0a3 100644
--- a/web/app/layout.tsx
+++ b/web/app/layout.tsx
@@ -60,8 +60,7 @@ const LocaleLayout = async ({
             <TanstackQueryIniter>
               <ThemeProvider
                 attribute='data-theme'
-                forcedTheme='light'
-                defaultTheme='light' // TODO: change to 'system' when dark mode ready
+                defaultTheme='system'
                 enableSystem
                 disableTransitionOnChange
               >
diff --git a/web/app/signin/_header.tsx b/web/app/signin/_header.tsx
index c7b1e67092..d2e3236d1d 100644
--- a/web/app/signin/_header.tsx
+++ b/web/app/signin/_header.tsx
@@ -2,6 +2,8 @@
 import React from 'react'
 import { useContext } from 'use-context-selector'
 import Select from '@/app/components/base/select/locale'
+import ThemeSelector from '@/app/components/base/theme-selector'
+import Divider from '@/app/components/base/divider'
 import { languages } from '@/i18n/language'
 import type { Locale } from '@/i18n'
 import I18n from '@/context/i18n'
@@ -10,17 +12,22 @@ import LogoSite from '@/app/components/base/logo/logo-site'
 const Header = () => {
   const { locale, setLocaleOnClient } = useContext(I18n)
 
-  return <div className='flex w-full items-center justify-between p-6'>
-    <LogoSite />
-    <Select
-      value={locale}
-      items={languages.filter(item => item.supported)}
-      onChange={(value) => {
-        setLocaleOnClient(value as Locale)
-      }}
-    />
-
-  </div>
+  return (
+    <div className='flex w-full items-center justify-between p-6'>
+      <LogoSite />
+      <div className='flex items-center gap-1'>
+        <Select
+          value={locale}
+          items={languages.filter(item => item.supported)}
+          onChange={(value) => {
+            setLocaleOnClient(value as Locale)
+          }}
+        />
+        <Divider type='vertical' className='mx-0 ml-2 h-4' />
+        <ThemeSelector />
+      </div>
+    </div>
+  )
 }
 
 export default Header
diff --git a/web/i18n/en-US/common.ts b/web/i18n/en-US/common.ts
index 0811ba73ff..66949f7276 100644
--- a/web/i18n/en-US/common.ts
+++ b/web/i18n/en-US/common.ts
@@ -1,4 +1,10 @@
 const translation = {
+  theme: {
+    theme: 'Theme',
+    light: 'light',
+    dark: 'dark',
+    auto: 'system',
+  },
   api: {
     success: 'Success',
     actionSuccess: 'Action succeeded',
diff --git a/web/i18n/ja-JP/common.ts b/web/i18n/ja-JP/common.ts
index 8a47801f58..1c31359485 100644
--- a/web/i18n/ja-JP/common.ts
+++ b/web/i18n/ja-JP/common.ts
@@ -1,4 +1,10 @@
 const translation = {
+  theme: {
+    theme: 'テーマ',
+    light: '明るい',
+    dark: '暗い',
+    auto: 'システム',
+  },
   api: {
     success: '成功',
     actionSuccess: 'アクションが成功しました',
diff --git a/web/i18n/zh-Hans/common.ts b/web/i18n/zh-Hans/common.ts
index 9c822885e0..c2d43e21a0 100644
--- a/web/i18n/zh-Hans/common.ts
+++ b/web/i18n/zh-Hans/common.ts
@@ -1,4 +1,10 @@
 const translation = {
+  theme: {
+    theme: '主题',
+    light: '浅色',
+    dark: '深色',
+    auto: '自动',
+  },
   api: {
     success: '成功',
     actionSuccess: '操作成功',