Supported Pt catalysts were prepared using several kinds of TiO2 supports different in the crystallite size in the range of 10 -500 nm and their catalytic activity was tested for the liquid-phase hydrogenation of 3-nitrostyrene, nitrobenzene, and styrene. With Pt on smaller TiO2 crystallites (nanocrystals), the selectivity to vinylaniline was improved in the hydrogenation of 3-nitrostyrene (regioselective hydrogenation) and the selectivity to aniline was promoted in the hydrogenation of a mixture of nitrobenzene and styrene (chemoselective hydrogenation). The effects of TiO2 crystallite size were discussed on the basis of the results of turnover frequency and FTIR of CO adsorbed on dispersed Pt particles.Low coordinated and/or electron-rich Pt sites should be formed on the surface of nanocrystal TiO2 supports. Nanocrystal TiO2 support is an important factor for controlling and improving the catalytic performance of dispersed Pt particles.