Abstract: Sulfate-reducing bacteria(SRB)was isolated from the sediments of the oxidation pond of Ya-Er Lake hubei, a heavily polluted lake by direct discharge of chloralkali effluent, and incubated in the laboratory. Its physiology characteristics and the effects of environmental factors were studied.The results show that temperature, pH, salinity, ferrous iron and sulfide greatly affect their characteristics.The effects on bivalent mercury methylation of SRB in the simulative anaerobic aquatic system were investigated.The methylation conditions were optimized by the orthogonal experiment.Themercury methylations of SRBunder anaerobic and aerobic environment werestudied, as well as its abioticmethylation.And we also studied the effects on methylation of the single environmental factor.The mercury compounds were detected by HPLC. In this paper,we developed a simple and rapid method for in situ preconcentration of inorganic and organicmercury compounds in water samples.At the same time, this developed mothod was indicated to be applicable for detectingHg2+and MeHg in environmental water samples in this test.The results indicated that this SRB grows best under the optimum conditions, such as 35 e, pH510, 017% salinity, 015g/L ferrous iron, and without sulfide.Mercury methylation in aquatic environment mostly occurs under anaerobic condition, and is mediated by SRB. And the abiotic and aerobicmercury methylations are negligible. It has been found that microbial methylation in anaerobicaquatic environment is influenced by a wide variety of environmental factors.Thetemperature(35 e), pH(510) and salinity(017%) are themost important affecting factors for mercury methylation.In aquatic environment, Mercury may be one of the most hazardous contaminants. Its ecological and toxicological effects strongly dependent on its chemical species present. Species distribution and transformation processes in natural aquatic systems are controlled by various physical, chemical, and biological factors.Under the environmental conditions, inorganicmercury speciesmay be converted to many times more toxicmethylated forms such as methylmercury.So it is of great necessity and importance for us to study the microbial methylation process and their affecting factors in aquatic environment.