This study aims to investigate the effects of different concentrations of cadmium (Cd) (0-800 μM) on the growth, the photosynthetic performance, and the biochemical parameters of the Chlorophyta Picocystis sp. during 3 and 9 days. Results showed that this exposure did not inhibit the Picocystis growth during the first 3 days of treatment. Growth inhibition did not exceed 53%, which was recorded at high Cd concentrations (800 μM) after nine exposure days. Moreover, no inhibitory effect on the Picocystis sp. photosynthesis has been recorded during the three exposure days regardless the Cd concentrations. Lipid peroxidation was significantly increased at high Cd concentrations (500 and 800 μM) by 40 and 80%, respectively. Furthermore, the highest Cd concentration enhanced the thiol protein content, indicating no consequent protein oxidation. The exposure of Picocystis to Cd stimulated the antioxidant activities of catalase and ascorbate peroxidase. These results showed that Picocystis sp. has an impressive tolerance to Cd stress.