The Songmuwu Group is an important pre-Sinian stratigraphic unit in western Zhejiang. Its upper part is mainly composed of the basalt-rhyolite association whereas the middle and lower parts consist mainly of grayish purple and grayish green. The U-Pb dating of single-grain zircon from acid volcanics in its upper part yields ages of 827 Ma and 809 Ma. Thus it is determined that the upper part is equivalent to the volcanic - sedimentary unit of the Shangshu Formation in the Hangzhou-Xiaoshan area. The arenite association in the middle and lower parts should be the equivalent of the Hongchicun Formation based on the comparison of lithologic associations. In order to simplify the names of the stratigraphic units in the Proterozoic Jiangnan orogen it is suggested that the name of the Songmuwu Group should be abolished and that this lithostratigraphic unit be called the Shangshu and Hongchicun Formations.