The hydrogenation of C=N was studied on the mesoporous carbon (CMC) supported Pd, Ru, and Ni catalysts by using diisopropylimine (DIPI) as a probe molecule. The microcalorimetric adsorption results demonstrated that the CMC possessed quite strong surface acidity which catalyzed the decomposition of DIPI that led to other subsequent side reactions. However, as long as the hydrogenation activity of a supported metal was high enough, the decomposition of DIPI could be inhibited, leading to the increased selectivity to the hydrogenation of DIPI. In particular, the Pd/CMC was found to be highly active and selective for the hydrogenation of DIPI and might be a preferred option for the hydrogenation of C=N double bonds.