Diffusion bonding method of chromium-copper alloy having a stable oxide layer was developed to improve tensile strength with low deformation of a specimen. In a manner of breaking the oxide layer by means of pressing, the tensile strengths were not well obtained and the specimens were moreover deformed. As the reason, contained chromiums were moved onto the bonding surfaces from bulk and subsequent oxidized with heating even in vacuum. It could be suppressed when the roughness of bonding surfaces was significantly smoothed. The specimens with smoothing surfaces were diffusion-bonded at 1073~1173 K for 3.6 ks without pressing. All the bonded specimens were fractured at the base metal. The bonded interface in the specimen fabricated at 1173 K could not specified on the SEM image. Also, the diffusion bonding was carried out with inserting a nickel film between the bonding surfaces in order to identify mutual diffusion. Nickel was theoretically diffused into chromium-copper alloys. It proved that metallic bonds were achieved between the bonded surfaces. However, a chromium oxide layer are easy to be generated at room temperature in atmosphere. The oxide layers had been already formed around chromium precipitations existing on the bonding surfaces before diffusion bonding. It was found that these cohered with heating, which enable the specimens to increase the bonded area. On the other hand, grain boundary migration over the bonded interface was not partly occurred in the specimen fabricated at 1073 K. An oxide and a void have been known to prevent the migration. In the case of diffusion bonding at 1173 K, the bonded interface disappeared by the migration in spite of residual oxide aggregations. Therefore, the void would be responsible for delaying the migration.