Abstract: Photodegradation of 17α-ethynylestradiol(EE2) in water by Fe(Ⅲ)/oxalate system was investigated under a 125 W high-pressure mercury lamp.The influence of initial pH,initial mass concentrations of EE2 and Fe(Ⅲ)/oxalate ratio on photodegradation efficiency of EE2 were discussed in detail.The results indicate that Fe(Ⅲ)/oxalate system can induce photodegradation of EE2.The degradation efficiency of EE2 is 53.5% after a 160 min radiation under the conditions of pH 3.50 and Fe(Ⅲ)/oxalate ratio 10.0/120.0.The optimum pH for degradation of EE2 in water is 3.00～4.00 over range of pH 3.00～6.00 in the experiment;under the initial mass concentration of EE2 of 2.0～10.0 mg/L,the photodegradation efficiency decreases with the increase of the initial concentration of EE2.