Saccharomyces cerevisiae J-5 was used as original strain for mutation breeding. A mutant strain J-5-9 which RNA content was higher than that of strain J-5 was selected. RNA content in shake flask was up to 13.12%, which was 10.62% higher than that in original strain. With molasses as carbon source, by orthogonal experiments, the fermentation medium components were optimized. The optimum conditions were molasses 3%, yeast extract 2%, KH_2PO_40.01%, monosodium glutamate 0.2%, ferrous sulfate 0.1%. Under the c...