A high T//c superconductivity was confirmed in an oxide mixed phase system of Y-Ba-Cu-O. The resistivity drop set in at 95 K, went through the mid-point at 90 K and finalized at 75 K. Furthermore, the diamagnetism as large as 5% of the complete Meissner effect was observed below 90 K, indicating the superconductivity to be of a bulk nature rather than a filamentary or interfacial one.