Abstract: Using the pretreated polyethyleneimine(PEI) as a polymer complexant,the effects of pH,loading ratio(L),ion strength and PEI concentration on polymer enhanced ultrafiltation process of rare earth wastewater containing La~(3 ) and Eu~(3 ) were discussed.Under pH=2.5,the complexation capacities of PEI to Eu~(3 ) was 0.5 mg/mg.pH and L had the similar trend on the retention of rare earth ions.The salt concentration in rare earth wastewater had the effect on the retention of rare earth ions.Under the volume diluted factor VDF=3,the recovery efficiency of PEI was more than 92% in the constant volume ultrafiltation process.The recovered PEI was reused for polymer enhanced ultrafiltation process of rare earth wastewater containing La~(3 ) and Eu~(3 ) and its recovery efficiency was the same as the fresh PEI.The retention of Eu~(3 ) for La~(3 )/Eu~(3 ) mixture solution almost was not affected under the high La~(3 ) concentration.Therefore,La~(3 ) and Eu~(3 ) might be selectively separated by polymer enhanced ultrafiltation method.