The effects of various reaction parameters on the catalytic activity and stereoselectivity in the hydrogenation of the isomeric xylenes over a silica-supported polysilazane-platinum complex (Si-N-Pt) have been studied. The ratio of cis and h-ans dimethylcyclohexane is a function of the structure of the substrate, temperature and catalyst concentration etc. cis-Dimethylcyclohexane is the more favored product for each of the three xylene isomers. The cis/trans ratio drops in the following order: o-xylene > m-xylene > p-xylene. The proportion of the cis isomer decreases with elevating temperature or decreasing substrate/catalyst mole ratio.