This work investigates mass transport in pervaporation dehydration of ethanol-water mixture with CS/HEC composite membrane. The analysis employed the pervaporation data obtained over a wide range of experimental conditions together with the resistance-in-series model, and the concentration dependent diffusion equations. The results reported are transport resistances for components, plasticizing and coupling coefficients. Transport resistances for the top membrane layer were much higher than other resistances which implied that transport in the dense membrane layer was the controlling step. Resistance for transport of water in the top layer was relatively low compared with that of ethanol. Plasticizing coefficients for water-membrane (k(ii)) were positive and those of ethanol-membrane (k(jj)) were negative indicating that water plasticized CS/HEC membrane but ethanol did not. The coupling coefficients obtained confirmed that ethanol reduced diffusivity of water in the membrane and the presence of water enhanced ethanol diffusion.