Dongdan Kingdom (926–936) (東丹, Khitan language: Dan Gur, Chinese: 东丹, Korean: 동란) was the puppet kingdom established by the Khitan to rule the realm of the Balhae in Eastern Manchuria (now partially in North Eastern China).
After conquering the Dan Gur (Balhae in Khitan language) in 926, the Khitan crown prince Yelü Bei ascended to the throne of it at the Holhan fortress, the capital of Balhae, today's Mudanjiang, Heilongjiang Province. It used Dongdan as its Chinese name, which means the east Dan Gur, in respect to the West Liao dynasty.
However, political tension soon evolved between Yelü Bei and his younger brother Yelü Deguang, who took the imperial throne of Khitan after their father Yelü Abaoji died, en route to his homeland from a relatively successful campaign against the Later Tang. The new emperor ordered his elder brother to move his capital from Huhan in Eastern Manchuria to Liaoyang in Western Manchuria.
Bei obeyed the imperial order but soon fled to North China to avoid possible assassination in 930. Bei's son was elevated to the new king of Dongdan, but the kingdom was annexed by the Liao Dynasty in 936.
To continue Balhae's friendly relations with Japan, Dongdan sent a diplomatic mission over the Sea of Japan (East Sea) in 929. But the Japanese court in Kyoto rejected the mission from Dongdan, due to loyalty for the old Balhae regime.