Abstract:Following the low dose of chlorine dioxide （1.0, 1.5,2.0,2.5 mg L-1） treatment of Phaeocystis globosa for 96 h and the high dose （2.5,6.0,8.0, 16.0 mg L-1） treatment for 60 min, the contents of chlorophyll a, proteins, amino acids and DNA in cells were determined. Meanwhile, changes in cell morphology after 24 h treatment of chlorine dioxide （0.5 mg L-1, 0.8 mg L--1） was observed by transmission electron microscope. Contents of chlorophyll a, proteins and DNA in the treated P. globosa were lower than those in controls. In the present of chlorine dioxide over 2.0 mg L-1, chlorophyll a, proteins, DNA in content and cysteine, tyrosine, lysine in relative percentage remarkably decreased, whereas histidine, valine and phenylalanine in relative percentage increased. The leakage rate of DNA was in the range of 13%-18% after treated with chlorine dioxide of 2.5-16.0 mg L-1 for 3 min. We observed that the substance damaged the cell membranes, causing the leakage of cellular content. These results suggested that chlorine dioxide might deform chlorophyll a and proteins in P. globosa by single molecular diffusion, damage the cell membrane system by lipid peroxidation, and eventually led to the death of cells.