Abstract: The effects of inoculum size,initial ammonia nitrogen concentration and initial glucose concentration on L-lysine fermentation was studied by 50 L fermenter test. The results showed that fermentation period was 40 h. The optimal culture conditions were as follows： 10% inoculum size,0.25% initial ammonia nitrogen, 3.5% initial glucose concentration. Under these culture conditions, the average yield of L-lysine was 175 g/L.