Abstract: Extracellular polysaccharide by Bacillus subtilis strain used in this study was isolated from Chinese yeast.The optimum culture medium for exopolysaccharide production by a Bacillus subtilis strain were primarily studied in the response surface method.First, optimum culture medium and additive amount were adopted by single factor experiments.On the basis of single factor experiment, the best carbon source, nitrogen source and inorganic salt were acquired by response analysis in which the exopolysaccharide production were the main indicators.The results indicated that the optimum composition medium was as follows:sucrose 25.449g/L, peptone bacto 15.229g/L, trisodium citrate dihyhrate 2.971g/L, beef extract 3.0g/L, magnesium sulfate 1.0g/L.Under the conditions, the production of extracellular polysaccharide by Bacillus subtilis was 3.554g/L.