A novel composite membrane with a three-layer structure has been prepared. The top layer is a thin dense film of chitosan crosslinked with glutaraldehyde, and the support layer is made of microporous polyacrylonitrile (PAN). Between the dense and the microporous layer, there is an intermolecular crosslinking layer. The performance data show that this is an excellent pervaporation membrane for alcohol dehydration and one-stage separation is attainable for some alcohol/water mixtures such as ethanol/water and isopropanol/water systems, which has a good separation factor of 1410 and a good flux of 0.33 kg m(-2) h(-1) for the EtOH/H2O mixture, and 5000 and 0.43 kg m(-2) h(-1) for the i-PrOH/H2O mixture using 90 wt-% alcohol concentration at 70 degrees C,Using 90 wt % methanol aqueous solution at 60 degrees C, a flux of 0.17 kg m-2 h-l and selectivity of 123 are also obtained. The structure and performance of the novel composite membrane varies with conditions of membrane preparation, such as hydrolysis degree of PAN membrane, content of crosslinking agent, and heat-curing temperature. The results indicate that the separation factor and the permeation rate of this novel composite membrane increase with the increase of operating temperature. At the same time, the pervaporation properties can be adjusted by changing the structure of the top layer and the middle layer. (C) 2000 John Wiley & Sons, Inc.