Removal of endocrine-disrupting chemical ethinylestradiol (EE2) from wastewater by microalgal mutant Chlorella PY-ZU1 under 15% CO2 were investigated. Moreover, the effects of EE2 on microscopic structure and antioxidation ability of microalgal cells were determined. EE2 concentrations in range of 0.01-5mg L-1 stimulated microalgal growth. Increasing the original EE2 concentration from 0 to 5 mg L-1 increased the cell fractal dimension from 1.38 to 1.59 and reduced the cell size from 5.18 to 3.41 mu m. Meanwhile, superoxide dismutase and catalase activities, which represented cellular antioxidant capacity, first increased from 44.59 and 0.54 U mL(-1) to peak values of 65.57 and 1.49 U mL(-1), respectively, and then correspondingly decreased to 34.36 and 0.36 U mL(-1). Malondialdehyde content that indicated the cell oxidation damage degree first decreased from 2.57 to 2.03 nmol mL(-1), then increased to 2.59 nmol mL(-1). The highest EE2 removal efficiency of 94% by Chlorella PY-ZU1 was achieved at the original EE2 concentration of 5 mg L-1.