The rejection properties of a nanofiltration organic membrane were investigated using KCl solutions, NaCl solutions, NaCl/benzyl alcohol hybrid solutions and KCl/benzyl alcohol hybrid solutions. The presence of benzyl alcohol (3.7mol.m(-3)) caused a decrease in electrolyte rejection within the range of 0 to 6%. The mechanism of the decrease was discussed. The cation-pi bond was assumed to formin the hybrid solution and to further induce the partial dehydration of the cation. The steric and charge density inhibition of the salt activity was strengthened, and the salt rejection was thus decreased. A simulation was performed to evaluate the radius of the cation. (c) 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.