Abstract: In order to improve the yield of poly γ-glutamic acid produced by Bacillus amyloliquefaciens fmbj37,the response surface methodology was performed to optimize the fermentation medium composition. Firstly,the importance of nine components of the medium was tested by Plackett-Burman(PB)experiments. Three critical factors related to the production of poly γ-glutamic acid,such as sucrose,sodium glutamate and dipotassium hydrogen phosphate,were selected based on the PB results. Then the concentration range of factors were carried out by the steepest climbing test. Finally,the optimal concentrations of sucrose,sodium glutamate and dipotassium hydrogen phosphate were determined by response surface analysis. The results showed that the optimal medium for producing poly γ-glutamic acid was composed of sucrose(115 g/L),sodium glutamate(59.35 g/L),dipotassium hydrogen phosphate(2.85 g/L),peptone(10 g/L),magnesium sulfate(1.5 g/L),potassium chloride(1 g/L),ferrous sulfate(0.0006 g/L),manganese sulfate(0.025 g/L)and copper sulfate(0.00064 g/L). In this medium,the yield of poly γ-glutamic acid reached(41.2±0.51) g/L,which was 6.9 times higher than before(5.2 g/L).