Abstract: In order to determine the interaction between nutrient concentration and simulated microgravity (SMG), Microcystisaeruginosa, cultured under rich and low nutrient medium (BG-11 and 1/10 BG-11 medium), were treated withdifferent gravity conditions. Both of M. aeruginosa in BG-11 and 1/10 BG-11 were sensitive to SMG. Their growth andmetabolism changed significantly after 2day-treatments. The effects of SMG varied significantly with the nutrient concentrationsof medium. For M. aeruginosa cultured in BG-11, SMG led to the decreased cell number and photochemicalefficiency of PS II as well as the increased cellular concentrations of chlorophyll a, carotenoid, phycocyanin, solubleprotein and microcystin. The SMG induced changes of cells in 1/10 BG-11 were contrary to the above-mentionedchanges of cells in BG-11. In1/10 BG-11, SMG led to the increased cell number and photochemical efficiency of PS IIas well as the decreased cellular concentrations of chlorophyll a, carotenoid, phycocyanin, soluble protein and microcystin.The effects of SMG and nutrient limitation were alike when they were applied to M. aeruginosa separately. Theinfluences of nutrient limitation were stronger than those of SMG. Under SMG, maybe the nutrient demand of cells wasreduced, as a result of the suppressed growth and photochemical activity. Otherwise, SMG might enable cells to usenutriments more effectively. Thus, SMG could alleviate the stress of low nutrient medium to M. aeruginosa. Collectively,these findings supported that the nutrient concentration of medium could significantly affect the responses of M.aeruginosa to SMG.