Tannu Uriankhai (Tuvan: Таңды Урянхай, Tuvan pronunciation: [tɑŋˈdə urjɑnˈxɑj]; Mongolian: Тагна Урианхай, romanized: Tagna Urianhai; simplified Chinese: 唐努乌梁海; traditional Chinese: 唐努烏梁海; pinyin: Tángnǔ Wūliánghǎi) is a historical region of the Mongol Empire. The realms of Tannu Uriankhai largely correspond to the Tuva Republic of the Russian Federation, neighboring areas in Russia, and a part of the modern state of Mongolia.

Tannu designates the Tannu-ola Mountains in the region. Uriankhai was the Mongolian name for the Tuvans (and accordingly their realm), which meant "the people living in the woods" (Chinese: 林中百姓; pinyin: Línzhōng Bǎixìng). After Outer Mongolia declared independence, the region of Tannu Uriankhai increasingly came under Russian influence and finally became an independent communist state, the Tuvan People's Republic, which was annexed by the Soviet Union in 1944 during the Eastern Front (World War II).

Referring to the 2001 Sino-Russian Treaty of Friendship, the People's Republic of China (PRC) has not officially renounced the sovereignty over the area, but just "have no remaining territorial claims" for two countries. But the PRC has official contacts with Tuva and regards it as part of Russia.