Manzhouli area is an important metallogenic province of Yanshanian porphyry-subvolcanic vein-epothermal mineralization series. The granites of the earlier stage serve as the main country rocks for ore depostis. It has always been questioned whether Indo_sinian granite exists or not in this area. In the adjacent area within Mongolia and Russia and in the Da Hinggan Mountains to its east there are Indo-sinian granites, but in Manzhouli-Xiqi area, Triassic synthem has not beens eparated out, and no definite age evidence has been sugggested.Some systematic petrological-mineralogical and Rb-Sr isotopic geochronological studies were carried out on the early stage granites from four major ore districts,which were previously considered to be late Hercynian or early Yanshanian. Two Rb-Sr isochron ages (225±7.9 Ma and 211±21Ma)obtained in this study show fine linear correlation,suggesting the existence of Indosinian granites. A considerable portion of originally-defined late Hercynian and early Yanshanian granites should be reassigned to Indosinian