In recent years, there was increased interest in the use of pervaporation membrane separation techniques for the selective separation of organic liquid mixtures because of the high separation efficiency coupled with potential savings in energy costs. The influence of the feed composition on ethanol dehydration by pervaporation is discussed in this study. The dehydration of ethanol-water mixture was carried out in a laboratory pervaporation unit with 110 cm(2) active surface by using different water permselective membranes (GFT-2000, CMC-CA-01, CMC-CE- 02). The experiments were performed at constant temperature (65 degrees C), flow rate (0.11 m s(-1)), permeate side vacuum (30 mbar) and the initial concentration of the feed mixture (80 wt% ethanol). The permeate flux, the ethanol and water cement in the permeate and in the concentrate fractions were measured during the experimental runs. Based on these measurements the pervaporation characteristics were determined: if there was an increase in the feed concentration, the permeate flux and the pervaporation separation index decreased, while the permselectivity and the separation factor increased. Comparing the separation behaviours of the membranes it was found that all the three types of membrane are suitable for ethanol dehydration by pervaporation and high concentration (99.64 wt%) ethanol product can be achieved.