The Old Uyghur language (traditional Chinese: 回鶻語; simplified Chinese: 回鹘语; pinyin: Huíhú yǔ) was a Turkic language which was spoken in the Kingdom of Qocho from the 9th–14th centuries and in Gansu where it evolved into the Western Yugur language.

The Old Uyghur language evolved from Old Turkic after the Uyghur Khaganate broke up and remnants of it migrated to Kashgar, Gansu and Turfan and Hami in the 9th century. The Uyghurs in Turfan and Hami founded the Kingdom of Qocho and adopted Manichaeism and Buddhism as their religions, while those in Gansu became subjects of the Western Xia.

The Kingdom of Qocho survived as a client state of the Mongol Empire, but was conquered by the Muslim Chagatai Khanatewhich conquered Turfan and Hami and Islamisized the region. The Old Uyghur language then went extinct in Turfan and Hami, but survived in Gansu where it evolved into the modern Western Yugur language.

Modern Uyghur is not descended from Old Uyghur, rather, it is a descendant of the Karluk language spoken by the Kara-Khanid Khanate.^[2] Western Yugur is considered to be the true descendant of Old Uyghur, and is also called „Neo-Uygur“.Modern Uyghur is not a descendant of Old Uyghur, but is descended from the Xākānī language described by Mahmud al-Kashgari in Dīwānu l-Luġat al-Turk.^[3] Modern Uyghur and Western Yugur belong to entirely different branches of the Turkic language family, respectively the southeastern Turkic languages and the northeastern Turkic languages .^[4][5]

Old Uyghur had an anticipating counting system and a copula dro, which is passed on to Western Yugur.^[6]

Much of Old Uyghur literature is religious texts regarding Manichaeism and Buddhism, with examples found among theDunhuang manuscripts. Multilingual inscriptions including Old Uyghur can be found at the Cloud Platform at Juyongguan and the Stele of Sulaiman.

Old Uyghur was written in the Old Uyghur alphabet which was derived from the Sogdian script.

• Arik, Kagan (2008). Austin, Peter, ed. One Thousand Languages: Living, Endangered, and Lost (illustrated ed.). University of California Press.ISBN 0520255607. Retrieved 10 March 2014.
• Chén Zōngzhèn & Léi Xuǎnchūn. 1985. Xībù Yùgùyǔ Jiānzhì [Concise grammar of Western Yugur]. Peking.
• Coene, Frederik (2009). The Caucasus – An Introduction. Routledge Contemporary Russia and Eastern Europe Series. Routledge. ISBN 1135203024. Retrieved 10 March 2014.
• Coene, Frederik (2009). The Caucasus – An Introduction. Routledge Contemporary Russia and Eastern Europe Series (illustrated, reprint ed.). Taylor & Francis. ISBN 0203870719. Retrieved 10 March 2014.

• Uyghur(Arghu)	Khalaj
  Uyghur(Karluk)	Aini1 Chagatai Ili Turki Lop Uyghur Uzbek
  Old Uyghur (Kipchak)	Ponto-Caspian (Crimean Tatar Cuman Karachay-Balkar Karaim Kipchak Krymchak Kumyk Urum2) Aralo-Caspian (Siberian Tatar Fergana Kipchak Karakalpak Kazakh Kyrgyz Nogai) Uralo-Caspian (Bashkir Old Tatar Tatar)
  Uyghur (Oghur)	Bulgar Chuvash Khazar Turkic Avar2
  Uyghur (Oghuz)	Afshar Azerbaijani Crimean Turkish Gagauz Balkan Gagauz Turkish Khorasani Turkic Old Anatolian Turkish Ottoman Turkish Pecheneg2 Qashqai Salar (Anatolian) Turkish Turkmen Urum2
  Old Uyghur (Siberian)	Altai Chulym Dolgan Fuyu Kyrgyz Khakas Old Turkic Old Uyghur Shor Tofa Tuvan Sakha/Yakut Western Yugur2 https://en.wikipedia.org/wiki/Old_Uyghur_language