Abstract: Objective:A strain with high-yield of the γ-PGA (γ-polyglutamic acid) was isolated and purified, and the fermentation conditions for the γ-PGA production were optimized. Methods:A strain of high-yield of γ-PGA production was isolated and identified from the soil around the tofu workshop, the strain was isolated and purified by plate dilution method, and then the strain was identified by the morphological and its 16S rDNA sequence. On the basis of single factor experiment, with temperature, pH, rotating speed and substrate concentration as experimental factors, the Box-Behnken method was adopted to optimize the fermentation conditions. Results:The strain was named as Bacillus siamensis. By the experiments of single factor and Box-Behnken design, the optimal culture conditions were as follows:Temperature 37.5℃, pH7.48, speed 240 r/min, substrate concentration 52.70 g/L, in the condition of shaking flask fermentation 36 h, γ-PGA yield was of 24.82 g/L, the substrate utilization of monosodium glutamate was 47.10%, increased by 25.19% than before optimization. Conclusion:It was convenient and feasible to optimize the fermentation conditions by the response surface method, which is beneficial to the further development and utilization of the γ-PGA.