The Qilian Mountains (also Nan Shan 南山 "southern mountains", viz., as seen from the Silk Road) is a northern outlier of the Kunlun Mountains, forming the border between the Qinghai and the Gansu provinces of northern China. The mountains are the source of the Ejin (Heihe) River.
The range stretches from the south of Dunhuang some 800 km to the southeast, forming the western border of the Gansu Corridor. Formerly the mountain range was named Richthofen Range after Ferdinand von Richthofen.
The eponymous Qilian Shan peak, situated some 60 km south of Jiuquan, at , rises to 5,547 m, constituting Gansu's highest elevation. It is the highest peak of the main range, but there are two higher peaks further south, Kangze'gyai at with 5,808 m and Qaidam Shan peak at with 5,759 m
The range continues to the west as Yema Shan (5,250 m) and Altun Shan (5,798 m). To the east, it passes north of Qinghai Lake, terminating as Daban Shan and Xinglong Shan near Lanzhou, with Maoma Shan peak (4,070 m) an eastern outlier. Sections of the Ming Dynasty's Great Wall pass along its northern slopes, and south of northern outlier Longshou Shan (3,616 m).
The Shiji mentions the "Qilian or Heavenly (Tian) mountains" together with Dunhuang as the homeland of the Yuezhi. It is however possible that the name here refers to the mountains now known as Tian Shan, 1,500 km to the west, and Dunhuang to a mountain otherwise attested as Dunhong. Qilian (祁连) is identified as a Xiongnu word meaning "sky" by Yan Shigu, a Tang Dynasty commentator on the Shiji.