Au/Bi-Sr-Ca-Cu-O (BSCCO) were prepared by evaporating Au on the air-cleaved surfaces of 80 K-phase BSCCO single crystals and heating in Ar gas. The electrical contact resistance of the Au/BSCCO specimen decreased by heating at 400 in Ar gas. From the depth profiles of the specimens by X-ray photoelectron spectroscopy, we found that there was a reaction region (Ar+-sputter etching time is 0 to 2 min (20 )) on the surface of the Au/BSCCO specimen heated at 400, where Au diffused into the bulk of the BSCCO single crystals. The reaction region is thought to cause the decrease of the electrical contact resistance of the specimen.