The effect of carbon molecular sieve (CMS) incorporated into poly(vinyl alcohol) (PVA) on pervaporation of benzene/cyclohexane mixtures was studied. The characterization results showed that filling of CMS decreased the hydrogen bond interaction among PVA polymer chains and made chains more flexible and relaxed, which resulted in decreasing of PVA membrane crystallinity, and thus created higher free volume in the membranes. CMS filling effectively increased DS values of membranes in almost whole feed composition range. Due to the more relaxed polymer chain packing and stronger sorption ability, the permeation flux of CMS-filled PVA membranes increased effectively, but excessive filling would decrease the permeation flux. With increase of benzene weight fraction, operating temperature and feed flow rate, the permeation flux of benzene increased, while the separation factor decreased. Compared with unfilled PVA membrane (flux of benzene 21.87 g/m(2) h, separation factor 16.7), flux of benzene of PVA-CMS-06 membrane (mass ratio of CMS to PVA was 6%) increased remarkably to 59.25 g/m(2) h and separation factor increased to 23.21. (c) 2006 Published by Elsevier B.V.