Abstract: Low temperature N2 plasma treatment was applied onto the surface of chitosan-polyacrylonitrile composite nanofiltration membrane. The membrane surface hydrophilicity and morphology were measured by contact angle, scanning electron microscopy and scanning probe microscopy. Chemical composition on the membrane surface was detected by X-ray photoelectron spectroscopy. The membrane filtration performance was evaluated by γ-aminobutyric acid solution concentration. It was demonstrated that treatment of 50 W and 20 Pa N2 plasma for 2 min ultimately improved hydrophilicity of the chitosan membrane and decreased its contact angle from 102.0° to 44.3°, it improved the membrane levelness as well. Chemical bonds on the membrane surface such as C—C, C—O, N—CO were reduced and —NH2, CO were increased. The flux of w=1.0% γ-aminobutyric acid solution through the membrane was enhanced from 1.12 L/(m2·h) to 1.75 L/(m2·h), meanwhile, at pH=6.15, the rejection of amino acids was improved from 28% to 83%.