Abstract: The effects of different concentration Pb²⁺(0.1,1,10,50,100,200,400 mg/L)in BG11 on the growth,morphostructure and physiological characteristics of Chlorococcum sp.were studied.Compared with the cell cultured in BG11,the cell cultured in low concentrations(≤50 mg/L)showed few changes in pigment and thickness of cell wall;the cell wall of the cell cultured in high concentrations of Pb²⁺(>50 mg/L)became thicker,and the pigment decreased and the pyrenoid disappeared.When the concentrations of Pb²⁺ were 0.1-10 mg/L,the growth of Chlorococcum sp.showed no obvious difference compared with the control;when the concentration of Pb²⁺ was 50 mg/L,Chlorococcum sp.could maintain certain growth rate yet;however,when the concentration of Pb²⁺ was higher than 100 mg/L,the growth of Chlorococcum sp.was inhibited markedly.The contents of Chl a+Chl b or Chl a decreased gradually with the increase of the concenrations of Pb²⁺ in the medium.The photosynthesis of Chlorococcum sp.decreased gradually with the increase of Pb²⁺ concentrations,when the concentration of Pb²⁺ was higher than 100 mg/L,the photosynthesis of Chlorococcum sp.could not be detected;when the concentration of Pb²⁺ was less than 50 mg/L,the respiration of Chlorococcum sp.increased gradually with the increase of Pb²⁺ concentrations,and when the concentration of Pb²⁺ was higher than 50 mg/L,they decreased gradually with the increase of Pb²⁺ concentrations.The content of malondiadehyde and activities of superoxide dismutase and peroxidase increased gradually with the increase of Pb²⁺ concentrations,and the activity of catalase increased at beginning and then decreased with the increase of Pb²⁺ concentrations.When the concentration of Pb²⁺ was ≤100 mg/L,the removal rate of Chlorococcum sp.on Pb²⁺ was >95%,and it was up 56.7% yet when the concentration of Pb²⁺ was 400 mg/L.The results demonstrated that the Chlorococcum sp.could be applied to the treatment of wastewater containing Pb²⁺,because the Chlorococcum sp.could endure the stress of Pb²⁺ and was of high removal rate on Pb²⁺.