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Ultra-fine silicalite-1 particles were modified with two kinds of chlorosilanes (dodecyltrichlorosilane and octyltrichlorosilane)and characterized with FI-IR，TGA，contact angle measurements and BET analysis. It was found that the surface hydrophobicity of silicalite-1 particles was improved significantly，with contact angle increasing from 16.4°(unmodified silicalite1)to 122.0°(modified silicalite-1 with dodecyltrichlorosilane). Modified silicalite-1 particles were incorporated into PDMS (poly (dimethylsiloxanediol))membranes，which were applied for the pervaporation of ethanol/water mixtures. The effect of zeolite loading and operation conditions on pervaporation performance of the membranes was investigated in detail. The separation factor of PDMS membranes filled with modified silicalite-1 increased considerably compared with that filled with unmodified ones，and the total flux decreased with increasing zeolite loading. The sorption and diffusion selectivity of filled membranes were also measured to explain the pervaporation properties of silicalite-1 filled PDMS membranes. It was found that modification of silicalite1 with dodecyltrichlorosilane effectively improved the sorption and diffusion selectivity of silicalite-1 filled PDMS membranes with high zeolite loading. This may be attributed to the high surface hydrophobicity of modified silicalite-1 and its good integration with PDMS membranes.Both of the high separation factor and sorption selectivity indicated that modification of silicalite-1 with chlorosilanes was an effective method to improve the selectivity of the zeolite filled PDMS membranes for ethanol/water mixtures.