diff --git a/decls/i18n.js b/decls/i18n.js
index ed1e3a093..e6d8dcdd6 100644
--- a/decls/i18n.js
+++ b/decls/i18n.js
@@ -85,6 +85,7 @@ declare interface I18n {
   set fallbackLocale (locale: Locale): void,
   get messages (): LocaleMessages,
   get dateTimeFormats (): DateTimeFormats,
+  get availableLocales (): Locale[],
   get missing (): ?MissingHandler,
   set missing (handler: MissingHandler): void,
   get formatter (): Formatter,
diff --git a/src/index.js b/src/index.js
index 1bef669df..b0aaa77b7 100644
--- a/src/index.js
+++ b/src/index.js
@@ -169,6 +169,7 @@ export default class VueI18n {
   get messages (): LocaleMessages { return looseClone(this._getMessages()) }
   get dateTimeFormats (): DateTimeFormats { return looseClone(this._getDateTimeFormats()) }
   get numberFormats (): NumberFormats { return looseClone(this._getNumberFormats()) }
+  get availableLocales (): Locale[] { return Object.keys(this.messages).sort() }
 
   get locale (): Locale { return this._vm.locale }
   set locale (locale: Locale): void {
diff --git a/test/unit/basic.test.js b/test/unit/basic.test.js
index db1f91da8..9fc548bc9 100644
--- a/test/unit/basic.test.js
+++ b/test/unit/basic.test.js
@@ -629,6 +629,12 @@ describe('basic', () => {
     })
   })
 
+  describe('i18n#availableLocales', () => {
+    it('should return locales defined in messages in lexical order', () => {
+      assert.deepStrictEqual(i18n.availableLocales, ['en', 'ja'])
+    })
+  })
+
   let desc = VueI18n.availabilities.dateTimeFormat ? describe : describe.skip
   desc('i18n#d', () => {
     let dt
diff --git a/types/index.d.ts b/types/index.d.ts
index a07abc15c..fee46e76c 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -141,6 +141,7 @@ declare class VueI18n {
   readonly messages: VueI18n.LocaleMessages;
   readonly dateTimeFormats: VueI18n.DateTimeFormats;
   readonly numberFormats: VueI18n.NumberFormats;
+  readonly availableLocales: VueI18n.Locale[];
 
   locale: VueI18n.Locale;
   fallbackLocale: VueI18n.Locale;
diff --git a/vuepress/api/README.md b/vuepress/api/README.md
index fc8820987..596e6ad52 100644
--- a/vuepress/api/README.md
+++ b/vuepress/api/README.md
@@ -209,6 +209,18 @@ The number formats of localization.
 
   * **See also:** `NumberFormats` type of [flowtype definitions](https://github.com/kazupon/vue-i18n/blob/dev/decls/i18n.js)
 
+#### availableLocales
+
+> :new: 8.9.0+
+
+  * **Type:** `Locale[]`
+
+  * **Default:** `[]`
+  
+  * **Examples:** `["en", "ja"]`
+
+The list of available locales in `messages` in lexical order.
+
 #### formatter
 
   * **Type:** `Formatter`