1INTRODUCTIONCharged membranes have been attracted more attention in membrane processes.Firstly,they have strong anti-fouling potential due to their charged groups.Secondly,they can be used as ion-exchange membranes for protein separations.Chitosan is the second abundant biopolymer after cellulose,and chitosan molecules contain a large number of reactive hydroxyl(-OH)and amine(-NH2)groups,therefore it can be an excellent candidate for affinity membranes[1].Until now,chitosan membranes have been used for reverse osmosis[2]，pervaporation[3],and ultrafiltration[4].And attempts have been made to improve blood compatibility of chitosan with physical blends,surface modification and synthesis of blood-compatible derivatives[5].The present work reports the preparation of a carboxymethyl amphoteric chitosan[poly(ethersulfone) (PES)/CM-CS]composite MF membrane and its charged characteristics.