A study of water on Pd/MgO(100) films prepared in situ upon Mo(100) single crystals has been performed by using low-energy electron diffraction, high-resolution electron energy-loss spectroscopy, and ultraviolet photoelectron spectroscopy in an ultrahigh vacuum system. The results show that the adsorption of water on MgO(100) film surfaces is enhanced significantly owing to the presence of Pd particles. The formation of a hydroxyl group suggests a dissociation of the water. The size and density of Pd particles on the substrate of MgO(100) films play an important part in the adsorption of water.