Abstract: It was studied that a strain of Lactobacillus. Sake BXR-5-3 which had high-yield of exopolysaccharides was mutagenized in different distance and time of ultraviolet ray, different concentration of nitrosoguanidine and composite mutagenesis by ultraviolet ray-nitrosoguanidine. It was showed that the best conditions for the composite mutagenesis was the distance of ultraviolet ray for 20cm, the time for 10min and the concentration of nitrosoguanidine for 300μg/mL, the yield of exopolysaccharides was 339. 0mg/L.