The effect of Mn2+ on the biotechmycin fermentation by Bioengineered strain WSJ-l-195 was studied. In the fermentation process, Mn2+ could improve the biological potency significantly, especially when Mn2+ concentration was 5 mmol/L added at 24 h. The pH profile of fermentation broth decreased gradually after 5 mmol/L Mn2+ supplemented at 24 h, and PMV was lower than that of the control sample. Further research about the influence of Mn2+ on the biosynthesis of biotechmycin was carried out in the aspect of organic acids. The results showed that concentrations of organic acids in a fermentation with 5 mmol/L Mn2+ supplemented at 24 h had been changed greatly, especially the concentration of propionic acid, of which the highest value was about 6 times as that in the control sample at 84 h. In addition, it was found that the yield of biotechmycin could be improved significantly with tiny amount of propionic acid added. Therefore, it can be concluded that Mn2+ has profound influence on the biosynthesis of biotechmycin: it enriches the biotechmycin precursor pool such as propionic acid and thus improves the yield of biotechmycin.