Abstract：The separation property of membrane is related to the aperture structure of the membrane. In this paper, the chitosan ultrafiltration (UF) membrane was immersed into a coagulation bath with proper concentration and temperature and its aperture structure was modified. The results showed that the retention rate of chitosan membranes increased by 83.7% after being treated by precipitation. The retention rate, flux and aperture structure of chitosan membranes were affected by temperature of the coagulation bath, concentration of gelating agents and time of immersion precipitation. It is necessary to select appropriate parameters to enhance the separation property of chitosan UF membrane.