Bayan-Ölgii aimag is located in the extreme west of the country, and shares borders with both Russia and China. The border between the two neighboring countries is very short here, though, and ends after about 40 km at the eastern end of Kazakhstan. Within Mongolia, the neighboring aimags are Uvs in the north east and Khovd in the south east..
Bayan-Ölgii is the highest Mongolian aimag. For the most part it is located in the Mongolian Altay, at the transition point to the Russian Altay. About 10% of the territory are covered by forests, consisting primarily of Siberian Larch.
The Tavan Bogd Uul (Five Saints Mountain) of the Tavan Bogd massif marks the corner between the three neighboring countries. About 2.5 km further south on the Mongolian-Chinese border, the Khüiten Peak (Cold Peak, also Nairamdal, Friendship Peak; Chinese: Youyi Feng) is the highest point of Mongolia with 4374 m. The massif includes several glaciers, such as the 19 km long named by Potanin, and is only accessible to experienced climbers with local guidance.
The River Khovd (the longest in the western Mongolian Great Lakes Depression) has its origin in this aimag. It is fed by the three lakes Khoton, Khurgan, and Dayan, and in turn feeds the lake Khar-Us Nuur in the Khovd Aimag. The Tolbo Nuur is a large saline lake about 50 km south of the aimag capital. It features clear and cold water on an elevation of 2080 m.