Experimental research for decreasing the wear of a resin-bonded diamond wheel was conducted for the mirror grinding of dies and molds. The gripping strength of diamond grains to the bond material was increased by modifying grain surfaces with an SiO 2 film using radio-frequency sputtering. In addition, the adhesion strength in both the surfaces between grain/SiO 2 film and SiO 2 film/bond material was increased using the plasma activation technique and a silane coupling agent. It was made obvious that the construction and composition of the SiO 2 film could be controlled by varying the sputtering conditions, such as working gas pressure, mixture rate of argon and oxygen gases. In particular, when the working gas pressure was low, the grain surfaces were covered with thin films with 20 nm Ry surface roughness. The grinding test revealed that the superficial area of diamond grains increased conspicuously and chemical binding between grain surfaces and bond material was generated, so that wear resistance superior to that obtained using conventional nickel plated grains can be derived.