Cd²⁺ is a serious environmental pollutant. Previous studies have investigated the effects of Cd²⁺ on animals, plants and algae. However, the tested concentrations were generally higher than the actual environment level. The present study determined the effects of low concentrations of Cd²⁺ (0.05 to 0.20 mg/L) on the chlorophyll fluorescent parameters of six local algae species in order to investigate the early toxicity of Cd²⁺. The results showed that treatments with up to 0.20 mg/L Cd²⁺ did not significantly affect population growth rate of S. quadricauda, C. pyrenoidosa, S. obliquus, N. palea, S. minutum and S. acutus. Treatments with 0.05-0.20 mg/L Cd²⁺ significantly increased F_v/F_m in N. palea and S. minutum and decreased F_v/F_m in S. obliquus and S. acutus, but did not significantly affect F_v/F_m in C. pyrenoidosa. When exposed to Cd²⁺, rETR_max was reduced in S. obliquus, C. pyrenoidosa, S. acutus and S. quadricauda, but was elevated in N. palea and S. minutum. Overall, trace Cd²⁺ still revealed early toxicity to green algae. N. palea, S. minutum and C. pyrenoidosa were more tolerant to Cd²⁺ than S. obliquus, S. acutus and S. quadricauda.