A novel positively charged composite nanofiltration (NF) membrane was developed and fabricated with cross-linked quaternized polyvinyl alcohol (q-PVA) as the active layer and polysulfone (PS) as the base support. The crosslinking was achieved by reacting q-PVA with 1,6-hexamethylene diisocyanate (HDI) at ambient temperature. Rejection performance of q-PVA composite NF membrane was measured as functions of quaternization degree (QD), q-PVA concentration, and the addition of low-molecular-weight inorganic electrolyte. It was found that the rejection of q-PVA/PS composite NF membrane for both inorganic electrolytes of MgCl2 and Na2SO4 increased with increasing QD. The q-PVA membrane showed 89.2 % of rejection and 10.3 kg m(-2) h(-1) of permeate flux to 5 mM MgCl2 solution at q-PVA concentration of 2.0 wt%. The rejections of q-PVA membrane for inorganic electrolytes followed the order: CaCl2 > MgCl2 > MgSO4 > NaCl > Na2SO4, agreeing well with Donnan exclusion theory.