Onon-Balj National Park (Mongolian: Онон Балж) covers two sectors of the Onon River valley as it flows north from Mongolia into Russia.

The area is one of relatively high biodiversity, and is also historically and culturally important for its association with Genghis Khan.

[1][2][3] The park covers mid-sized mountains and confluence of the Onon and Balj Rivers.

[6][7] The park is in southern extent of the Trans-Baikal conifer forests ecoregion.

[8] The park has been designated an Important Bird Area by BirdLife International; birds known to breed there include the vulnerable Swan Goose (Anser cygnoides), Lesser kestrel (Falco naumanni), and the vulnerable White-naped crane (Antigone vipio).