Abstract: The Middle Proterozoic in the Bajiazi area, Jianchang, Liaoning province, may be divided in ascending order into the Dahongyu Formation, Gaoyuzhuang Formation, Datun Formation and Wumishan Formation, of which the Datun Formation is a newly established one. The Dahongyu Formation, 589 m thick, consists of quartz sandstone and conglomerate in the lower part and quartz sandstone, shale, tuffaceous sandstone and tuff in the upper, locally intercalated with dolomite. The Gaoyuzhuang Formation, 337 m thick, is composed of dolomite with chert bands, yielding Conophyton garganicum and C. cylindricum in the lower part, manganese-bearing clastic rocks and dolomite in the middle and platy dolomite in the upper. The Datun Formation, 773 m thick, is mainly made up of gray thin-bedded sandy micritic dolomite. The top is marked by unstable purplish gray dolomite and the base yields Conophyton garganicum Koroljuk et al. It is stratigraphically equivalent to the Yangzhuang Formation. For lack of a very thick bed of red shale, a new formation is set up and named the Datun Formation. The Wumishan Formation, over 198 m in thickness, is lithologically represented by dolomite with chert hands. The stratigraphical sequence, lithology and stromatolite features of the Middle Proterozoic in the Bajaizi area, Jianchang, can be correlated with those of the corresponding strata at the Jixian stratotype section, Its sediment type is of Jixian type.