In this work, the effect of copper and zinc on green alga Pseudokirchneriella subcapitata was evaluated through catalase activity, lipid peroxidation by TBARS essay, growth rate, and the chlorophyll-a concentration. Catalase activity increased significantly (P < 0.05) in comparison to the control at 0.1 mg L-1 copper and 0.075 mg L-1 zinc, whereas the damage to the cell membrane expressed as nmols/10(6)cell of malondialdehyde increased significantly (P < 0.05) at 0.025 mg L-1 copper and 0.1 mg L-1 zinc. On the other hand, a significant (P < 0.05) decrease in chlorophyll-a concentration was found at 0.075 mg L-1 of both metals. The results showed that catalase activity, lipid peroxidation, and chlorophyll-a concentration were more sensitive to metals than the growth rate.