Carboxylic-functionalized carbon nanofiber-supported Ru catalysts were prepared from the treatment of carbon nanofiber in HNO3-H2SO4 media, followed by impregnation with RuCl3 solution, dryness, calcination, and reduction procedures. Interestingly, carboxylic-functionalized carbon nanofiber-supported Ru catalysts show a good performance in oxidation of benzyl alcohol with molecular oxygen. In contrast, after partial removal of carboxylic groups on the surface of carbon nanofiber-supported Ru catalysts, the activities are reduced significantly. These results suggest that the carboxylic species on carbon nanofiber-supported Ru catalysts play an important role for the promotion of catalytic activity.