A poly (acrylic acid)-polyacrylonitrile (PAA-PAN) composite membrane was evaluated for the separation of water-ethanol mixtures by pervaporation, and the separation characteristics were investigated in relation to the preparation conditions of the PAN composite support layer and the addition of aluminum nitrate to the PAA coating solution. The composite membrane had a water permselectivity in the range 20-95% of ethanol feed concentrations in our experiment; in particular, the separation factor was high at higher ethanol concentrations. The maximum separation factor was 30,000 at an ethanol feed concentration of 95 wt%. The membranes showed a maximum separation factor with a 100,000 molecular weight cut-off of the PAN support layer. The dependence of the separation properties on the aluminum nitrate concentration in the PAA coating solution exhibited a maximum at 0.1 mass ratio.