The effects of fermentation temperature,the initial pH of fermentation broth,shaking speed and feeding time on the cell dry weight and yield of S-adenosyl-L-methionine (SAM) produced by Saccharomyces cerevisiae (A12A,A18A) selected from 45 yeast strains were studied,and the fermentation conditions was optimized.The results showed that cell dry weight and SAM production were significantly affected (P<0.05) by fermentation temperature,the initial pH,rotation speed and the feeding time.With the orthogonal optimization,the most suitable conditions for SAM accumulation are temperature 25 ℃,initial pH 6.0,shaking speed 225 r/min,and feeding time 108 h.Under fermentation conditions mentioned above,the SAM production of Saccharomyces cerevisiae A18A was up to 2.54 g/L broth,1.17-fold higher than before optimization.