Abstract: To investigate physical chemical condition, composition of microbial population, rates of sulfate reduction and methanogenesis in formation water of the block 1 of Kongdian Oilfield to study potential of microbial enhanced oil recovery. The amount of thermophilic aerobic saprotrophs,hydrocarbon-oxidizing bacteria,anaerobic fermentative bacteria, sulfate-reducing and methanogenic bacteria in injection and formation water were determined by most-probable-number(MPN) method. the sulfate reduction and the rate of methanogenesis processes were analyzed by radioisotopic method. The results show vary microflora inhabited in the block 1 of Kongdian Oilfield. The numbers of thermophilic aerobic saprotrophs and hydrocarbon-oxidizing bacteria in the injection water reached to 105 cells/mL and 103 cells/mL respectively. The population density of anaerobic fermentative bacteria in the injection water reached to 107 cells/mL, and sulfate-reducing bacteria reached to 102 cells/mL Methanogenic bacteria were range from 1 to 10 cell/mL. Five kinds of bacteria above were also presented in production wells. So it is possible to enhance oil recovery by activating indigenous microbial of hydrocarbon oxidizing, fermentative bacteria and methanogenic bacteria in this area.