Since discovery of the Y-Ba-Cu oxide compound showing superconductivity above liquid nitrogen temperature, intensive study has been under way to clarify nature of the high Tc oxides[l-4]. Much efforts were also made in the field of superconductor applications. A number of studies have been carried out by a powder metallurgical process of Y-Ba-Cu oxide compound wires, although, obtained critical current densities were still low at liquid nitrogen temperature[5–6]. Other techniques for wire fabrication is also being attempted[7–9]. In this study, Y-Ba-Cu oxide superconducting composite tapes were prepared by a diffusion process, which is one of the promising methods to obtain a high critical current density.