The Tannu-Ola mountains (Tuvan: Таңды-Уула, Tañdı-Úla - Tangdy-Uula mountains; Mongolian: Тагны уулс, Tagnī úls) is a mountain range in southern Siberia, in the Tuva Republic of Russia. It extends in an east-west direction and curves along the Mongolian border. Its highest peak reaches 2,930 m (9,610 ft).
The northern slopes are part of the watershed of the Yenisei River, facing the western Sayan Mountains. The eastern end touches the large watershed of the Selenge River in Mongolia. The foothills of the southern slopes cross into Mongolian territory. They form the northern limits of a large basin of steppes that extends south to the Mongolian Altay Mountains and includes the salt lake Uvs Nuur. The western end is located near the northern Altay Mountains in the Russian Altai Republic.