Gelular poly(vinylpyridine)-supported palladium catalysts and their analogue have been prepared, and used to study the mechanism of hydrogenation and the solvent effect on catalytic activities. When the polymer-supported Pd catalyst was used in the hydrogenation of cyclohexene, an induction period is observed. The hydrogenation occurs via heterolytic activation of hydrogen. The relationship between the rate of hydrogenation and the solubility parameter of the solvent shows a concave curve with a minimum value at which point the polymer and solvent have similar solubility parameters. The mechanism of hydrogenation of cyclohexene has been suggested.