Activities of ethylene/alpha-olefin copolymerization were found to increase with silane-modified silica-supported MAO using ansa-zirconocene catalyst. The increase in activities was less pronounced when higher alpha-olefins were used. However, silane modi. cation resulted in the narrower molecular weight distribution of polymers. C-13 NMR revealed that ethylene incorporation in all systems gave polymers with the similar triad distribution.