Abstract: A starting strain of Lactobacillus casei G5 was mutated by space mutagenesis technology to screen strains with high production of exopolysaccharides. Through enrichment culture, plate screening, skim milk fermentation and genetic stability experiment, we finally got two stable mutant strains EPS-33 and EPS-43 with high production of exopolysaccharides.while mutant strains EPS-33 and EPS-43 fermented in skim milk at25℃, the yield of exopolysaccharides were 220.42mg/L and 198.49mg/L, which were 1.9 and 1.7 times of starting strain. Exopolysaccharides production of the two mutant strains had the same change trend as starting strain, but the two mutant strains had a significant increase in production.