Abstract: In the western sector of the Northern Qilian Mountains, late Silurian conodonts, namely, Ozarkodina cf. remscheidensis eosteinhornensis （Walliser）and Synprioniodina cf. silurica Walliser, have been found in Member"q₃"of the upper part of the middle Silurian Quannaogoushan Group which was formerly determined by the Qilianshan Geological Team of the Chinese Academy of Sciences. In this paper, according to the age of the conodonts and the thological changes, Member "q₃"of the Quannaogoushou Group is assigned to the upper Silurian.