Abstract: Experiments were carried out to investigate the effects of light intensity(60, 120 and 200 μmol/(m²·s)), temperature(16, 22 and 28℃) and salinity(25, 30 and 35) on growth and paralytic shellfish poisoning(PSP) toxins production by Alexandrium tamarense HongKong strain(ATHK), A. minimum Taiwan strain(AMSY), A. catenella Nanhai strain(ACSY) and Gymnodinium catenatum Fangchenggang strain(GCFC). The results showed that 22℃ was the optimum growth temperature for all the four strains. Low temperature promoted PSP toxins production in all of the four strains. Except for GCFC, PSP toxins production in the other three strains were reduced with the temperature rising. The growth of ATHK and AMSY were positively correlated with light intensity. Toxin production in AMSY and GCFC were also positively correlated with light intensity. Toxicity of both ATHK and ACSY were also affected by light intensity, with maximum toxicity obtained at the light intensity of 120 μmol/(m²·s). Low light intensity inhibited toxin production in all of the four strains. ATHK, AMSY and GCFC all grew well at the salinity of 30, while ACSY grew well at the salinity of 35. Toxin production in ATHK increased with the increasing salinity. Both higher and lower salinities promoted the toxins production in AMSY and ACSY. A high level of toxin was detected in GCFC at the salinity of 30.