Heterogeneous Ru-Sn catalysts are effective for the liquid-phase hydrogenation of C=O group in carboxylic acids. Hydrogenation activity was affected by the kind of tin compounds used for the preparation of the Ru-Sn catalyst. Bis-tributyl tin oxide ((Bu3Sn)(2)O), K2SnO3 and Na2SnO3 were found to be the appropriate materials for the hydrogenation of C=O group over the Ru-Sn catalysts. The C=O hydrogenation activity for the hydrogenation of carboxylic acids increased with the increasing amount of Sn added whereas, the C=C hydrogenation activity decreased. Effect of activation temperature was also studied. The C=O hydrogenation activity was increased by calcinating the catalyst precursor, Sn/alumina, before impregnation with Ru solution. The calcination of the Sn/alumina at 973 K was quite effective for the hydrogenation of carboxylic acids over the resultant Ru-Sn/alumina catalysts. The Ru-Sn/alumina catalysts reduced at 723 K were also effective for the hydrogenation of carboxylic acids. We have also studied the hydrogenation in a continuously flowing system. The Ru-Sn/alumina catalysts showed high and stable activity under mild conditions in the flowing system.