Pervaporation is a promising membrane technique for separation of aqueous organic mixtures. In this study, ethanol water mixtures were dehydrated by the pervaporation. Hydroxyethyl cellulose (HEC) membrane was prepared by the solution casting method and cross linked with phosphoric acid in order to avoid dissolution in the mixture. Structure of HEC membrane was characterized by FTIR and SEM. The effects of experimental parameters such as feed concentration and operation temperature on total flux and separation factor were evaluated. Flux increased with an increase in feed concentration of water in the mixture and operation temperature, but separation factor decreased. HEC membrane gave the highest separation factor of 27.55 with a flux of 0.975 kg/m(2)h at 50 degrees C for 5 wt. % of water in the feed mixture. The results showed that the HEC membrane was water selective. In addition pervaporation separation index and activation energy for water permeation were calculated and interpreted.