Among the various membrane processes, pervaporation is an effective process for separating the species of aqueous mixtures particulary azeotropic and close-boiling mixtures. Because the membrane is recognized as the most important part of the pervaporation process, some modification should be used to acquire membranes with better mechanical and thermal resistance as well as separation properties such as permeation flux and separation selectivity. Among different methods for membrane modification, cross-linking is widely attended by the researchers. In the present work, poly(vinyl alcohol) membranes were cross-linked at 150°C by using fumaric acid as the cross-linking agent and the effect of cross-linking time on the membranes’ properties was investigated. The prepared membranes at three different time of 10, 30 and 60 min were characterized by different known methods of FT-IT, TGA, XRD, SEM as well as tensile test. Formation of more ester groups owing to the reaction between fumaric acid and poly(vinyl alcohol) was confirmed by the FT-IR results. TGA analyses showed the thermal stability of the membranes was improved by prolonging the duration of cross-linking time due to the formation of membranes with more compact structure. Also, the XRD results revealed that the crystalline regions of the membranes were relatively diminished and amorphous regions increased with increasing the cross-linking time. The SEM images showed that increasing the cross-linking time had no effect on the surface morphology and only led to a more compact structure. No special trend can be seen for the variation of tensile strengh with cross-linking time. The synthesized membranes were used for dehydration of water/isopropanol mixtures for investigation into effect of cross-linking time effect on the separation properties of the cross-linked membranes. The membranes cross-linked for 60min showed high selectivity of 1492. Lower value of E pw in comparation with E pIPA supported excellent dehydration performance of the cross-linked membranes. In the second part of this study, the mixed matrix membrane consisting of poly(vinyl alcohol) polymer and different amounts of NaX zeolite particles were prepared to improve separation properties of the cross-linked membranes. The incorporation of zeolite particles into the polymer matrix was confirmed by the observation the FT-IR spectra related to NaX zeolite. TGA results indicated that the thermal stability of mixed matrix membranes increased effectivily with increasing the zeolite content from 10 to 30 wt%. The addition of zeolite loading to more than 30 wt% led to formation of the brittle mixed matrix membranes with no effective application. On the basis of XRD patterns, the incorporation of zeolite particles to polymer matrix avoided from formation of crystalline regions and as a results amorphous regions were more than crystalline regions in mixed matrix membrane which was in favor of permeation through the membranes. According to mechanical tests, increasing the zeolite loading in the polymer matrix improved the mechanical stability of the resulting mixed matrix membranes. These membranes were used for separation of methanol/MTBE mixture by pervaporation to understand the effect of zeolite incorporation in polymer matrix on it’s PV performance. The pervaporation results showed a simultaneous enhancement in flux and selectivity upon adding zeolite in membrane matrix. Flux of pristine membrane was 0.0499kg/m 2 .hr and selectivity of 174 ,while corresponding values for the mixed matrix membrane containing 30 wt% of zeolite were 0.085 kg/m 2 .hr and 634, respectively. In addition of zeolite content, effects of operating conditions such as feed composition and temperature on the membrane performance were studied. It was observed that permeation flux increased with increasing methanol concentration in the feed mixture as well as process temperature whereas both had negative effects on the selectivity. Arrhenius plots were drawn to comput the activation energies for the total permeation flux as well as partial fluxes of methanol and MTBE. The activation energies of total flux and methanol flux were found to be almost close to each other, supporting that the mixed matrix membranes developed in this work were highly methanol selective and can be effectivily useful for separation of methanol/MTBE mixture. Keyword: Poly(vinyl alcohol), Fumaric acid, Cross-linking, M ixed matrix membranes, NaX zeolite.