Abstract：The Manzhouli area is an important metallogenic province of nonferrous and noble metals. The regional strata consist mainly of Mesozoic continental volcano-sedimentary formations. The Jiawula, Chaganbulagen and Eren Tolgoi Ag- (Pb-Zn) deposits all occur on the bottom of the strata. Previously there were disputes on the age of the host strata. The authors have further studied the characteristics of the host strata in the three Ag- (Pb-Zn) districts and in the Bayan Haolei Ag-polymetallic mineralization district and the strata of the Kanzijing section which plays a very important role in the stratigraphic division in the area. The results of the study indicate that the strata hosting the Ag- (Pb-Zn) deposits in the area are notably differerent from their overlying Late Jurassic Early Cretaceous strata in respect of the rock association, stratigraphic sequence and geochemistry. The fossils discovered in the host strata and new geological research results in the area suggest that the age of the strata hosting the Ag- (Pb-Zn) deposits in the area is Late Triassic-Early Jurassic.