The assays of first exposure and second exposure effects with tetracycline (TC) on the freshwater cyanobacterium Microcystis aeruginosa and chlorophyceae Selenastrum capricornutum were investigated by determining a battery of parameters including algal biomass, chlorophyll fluorescence index Fv/Fm, superoxide dismutase (SOD) and malonaldehyde (MDA) in this study. In general, TC could significantly inhibit the growth and physiological progress including primary photochemistry and antioxidant system. However, upon the second exposure, the inhibitory effects of TC were decreased compared to the first exposure. And it suggests that Fv/Fm, SOD and MDA were more sensitive than algal biomass. In addition, M. aeruginosa showed stronger survivability than S. capriconutum.