The Liaodong Peninsula (simplified Chinese: 辽东半岛; traditional Chinese: 遼東半島; pinyin: Liáodōng Bàndǎo) is a peninsula in Liaoning Province of Northeast China, historically known in the West as Southeastern Manchuria. Liaodong (formerly spelled Liaotung) means "East of the Liao River"; referring to the Liao River which divided the Yan commanderies of Liaoxi (simplified Chinese: 辽西; traditional Chinese: 遼西) (West of the Liao River) and Liaodong during time of the Warring States period.
The peninsula lies in the north of the Yellow Sea, between the Bohai Sea to the west and Korea Bay to the east.
It forms the southern part of a mountain belt that continues northward in the Changbai Mountains. The part of the mountain range on the peninsula is known as the Qianshan Mountains, named after Qian Mountain in Anshan, which includes Dahei Mountain in Dalian.
Liaodong came under the rule of the Gojoseon kingdom which emerged in the region. In the late 4th century BC, the Chinese State of Yan invaded and conquered this region from Gojoseon. Later on various states and dynasties such as the Han Dynasty, Gongsun Yuan, Cao Wei, Western Jin, Former Yan, Former Qin, Later Yan, Goguryeo, Tang Dynasty, Balhae, Liao Dynasty, Jin dynasty (1115–1234), Yuan Dynasty, Ming Dynasty and Qing Dynasty ruled Liaoning.