In this study, the responses of Microcystis aeruginosa growth to oxidation reduction potential (ORP) reducing were studied by momospecies culture and mixed culture with Scenedesmus obliquus. Cell size, esterase activity and chlorophyll fluorescence intensity of M. aeruginosa were measured by flow cytometry. The results showed that oxidation reduction potential of medium was reduced by exogenous glutathione (GSH). In monospecies culture groups, M. aeruginosa has a significant higher growth rate than S. obliquus, and no significant effects of ORP on the two algae were found. However, in mixed culture groups, the growth of the two algae were obviously inhibited and the cell concentration of M. aeruginosa was still dominant. While ORP was reduced, the growth rate of M. aeruginosa was enhanced and that of S. obliquus was inhibited. Furthermore, Cell size, esterase activity and chlorophyll fluorescence intensity of M. aeruginosa were increased after ORP was changed. All these changes play an important role in enhancing growth rate of M. aerugionsa.