Two series of novel composite nanofiltration (NF) membranes were prepared by the overcoating of polysulfone ultrafiltration membranes with a mixture of chitosan and chitosan derivatives modified with two different chiral compounds. The two chiral compounds and their chitosan derivatives were characterized by IR spectroscopy, differential scanning calorimetry, and polarimetry. The structure of the membrane was characterized by scanning electron microscopy (SEM). The rejection and flux of the composite NF membranes were strictly related to the chiral compound grafted to chitosan and its composition in the mixture. An extremely high rejection, 98.23%, was observed with P2-3 of the polymer (P2) composite NF membrane, and the flux remained as high as 351 L m-2 h-1 at 0.4 MPa with 1000 mg/L NaCl. These results, together with SEM and IR images of the composite NF membrane, indicated that the chiral compound structure was crucial for the structure and function of the composite membrane. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013