Abstract: A series of amphoteric polymeric electrolyte was prepared and their antibacterial activities and dissolving behaviour in water were investigated. A series of quaternized N,O-2-carboxyethyl chitosans(QCECs), which exhibit typical behaviour as amphoteric electrolyte, were obtained through the chemical modifications of N,O-(2-carboxyethyl) chitosan(N,O-2-CEC) by 2, 3-epoxypropyl trialkyl ammonium chlorides including glycidyl trimethyl ammonium chloride(GTMA), glycidyl triethyl ammonium chloride(GTEA), glycidyl tripropyl ammonium chloride(GTPA), glycidyl tributyl ammonium chloride(GTBA) and glycidyl dimethylbenzyl ammonium chloride(GDMBA). Substitution degree of quaternization(DQ) of QCECs was determined by the potentiometry, in which the variations of potential of solution with the volume of AgNO₃ aqueous solution were measured. The isoeletric points(pH_iep) of N,O-2-CEC and its quaternized derivatives were determined by spectrometry method. The antibacterial activities of chitosan derivatives including N,O-2-CEC and QCECs were evaluated according to their minimum inhibition concentrations(MICs) against E.coli, a typical Gram-negative bacterium, and S.aureus, a typical Gram-positive bacterium, determined by agar plate method. DQ values of QCECs were estimated in the range of 51.3%~59.1%, the pH_iep of N,O-2-CEC and QCECs were in the range of 6.44~7.30 and the introduction of quaternizing group resulted in the accretion of pH_iep. Except the product obtained from the modification of N,O-2-CEC by GTMA, the pH_iep values of all other QCECs increased along with their DQ contents. All N,O-2-CEC and their quaternized derivatives showed improved antibacterial activity against E.coli and S.aureus. The MIC values of QCECs were lower than those of N,O-2-CEC. The increase of carbon chain length of alkyl and the presence of dimethyl benzyl in the quaternary ammonium groups could endow QCECs with much better antimicrobial activity.