Hydrogenation of an ct, P-unsaturated aldehyde, cinnamaldehyde (CAL), was carried out with silica-supported platinum catalysts in ethanol under pressurized hydrogen atmosphere up to 12 MPa at 50 degreesC. The initial rate of reaction (CAL consumption) was proportional to hydrogen pressure and independent of CAL concentration. Increasing hydrogen pressure decreased the selectivity of cinnamyl alcohol (COL) but increased that of hydrocinnamaldehyde (HCAL). The COL selectivity increased with CAL concentration. The effect of hydrogen pressure on the selectivity in ethanol is different from that observed previously in a solvent of supercritical carbon dioxide.