The ring hydrogenation of 4-propylphenol in aqueous ethanol solution was studied over graphite- and activated carbon-supported palladium catalysts (Pd/G and Pd/C) with 0.1-5 wt % of palladium loadings without using external hydrogen. Decomposition of ethanol produced hydrogen which was responsible for the hydrogenation of 4-propylphenol over palladium metal particles on both the supports in aqueous medium. The different hydrogenation behaviors were discussed based on surface properties of supports.