The Pd catalysts were prepared by impregnating Pd(CH3COO)(2) in Al2O3 supports. To investigate the influence of mass transfer on the catalytic performance, the catalysts and the polystyrene-block-polybutadiene-block-polystyrene thermoplastic elastomers (SBS rubber) were prepared with average pore size ranging from 150 to 600 Angstrom and molecule weight ranging from 100 000 to 200 000. The test reactions were carried out in a semibatch basket type reactor at 500 psig and temperature ranging from 80 to 180 degrees C. The experimental results indicated that among the catalysts of different pore sizes, the catalyst with an average pore diameter of 389 Angstrom presented the highest conversion and selectivity to olefinic microstructures for the SBS rubber of 100 000 in hexane. The superior catalytic performance for the catalyst was regarded as the compromise between pore size and the Pd dispersion of the catalyst; catalyst having a larger pore has lower mass-transfer limitation whereas it also has poorer Pd dispersion. Elevating the reaction temperature promotes the hydrogenation rate but decreases the selectivity to olefinic microstructures. Furthermore, the catalytic performance of the catalyst was greatly influenced by the solvent of SBS. Catalyzed by the same catalyst, after hydrogenation, the SBS in toluene presented better quality than that in cyclohexane.