Structural parameters and electrical properties of nanofiltration membranes (Desal-5, NF-40, NTR7450 and G-20) were determined with permeation experiments of aqueous solutions of neutral solutes (alcohols and saccharides having different molecular weights) and sodium chloride. The pore radii of these nanofiltration membranes were estimated to range from 0.4 to 0.8 nm based on the steric-hindrance pore model. Neither the constant surface charge density nor the constant surface electrical potential were suitable for interpreting NaCl concentration dependency of reflection coefficients. The fixed charge density of these membranes was evaluated on the basis of the Teorell-Meyer-Sievers model; a simple empirical equation was proposed to represent the dependency of the fixed charge density on NaCl concentration.