Tuul River (Mongolian: Туул гол, tuul means "to wade through"; in older sources also Tola) is a river in central and northern Mongolia considered sacred by the Mongols. It is 704 km long and drains an area 49,840 square km. The river is called the "Duluo river" in the Suishu, a Chinese historical work completed in 636 AD. The Secret History of the Mongols (1240 AD) frequently mentions a "Black Forest of the Tuul River" where the palace of Wang Khan was located (Genghis Khan visited it frequently and later made it his own). The Tuul is generally called the Khatan Tuul or Queen Tuul, similar to the Onon River, which is called Onon Khatan Ijii or Queen Mother Onon.

Originating in the Khan-Khentein-Nuruu Nature Reserve in the Khentii Mountains, this body of water runs through the southern part of the Mongolian capital of Ulaanbaatar. It is a tributary of the Orkhon River, which flows into the Selenge River, which flows into Russia and Lake Baikal. The Tuul River also flows along the Khustain Nuruu National Park. It is typically frozen over from the middle of November through the middle of April. Willow forests grow along the Tuul River, and the river itself is home to endangered species of sturgeon.^{[citation needed]}