The size-controlled Cu nanoparticles having average particle size of 4.5, 6.3, and 7.3 nm were prepared on ZnO/SBA-15 mesoporous silica by microwave-assisted alcohol reduction in the presence of surface-modifying ligands possessing different carbon chain length such as sodium laurate (C, 12) and sodium stearate (C, 18), and the efficient hydrogenation reaction of p-nitrophenol to p-aminophenol was achieved by the Cu/ZnO/SBA-15 having Cu nanoparticles with appropriate size.