Superconducting transition and critical current of a Y‐Ba‐Cu‐oxide compound prepared by ceramic technique have been studied for the samples which have the same nominal composition and sintering conditions, while systematically varying the calcining temperature from 850 to 1000 °C. It was observed that the shape of the superconducting transition in resistivity measurement markedly depends on the calcining temperature. All samples showed metallic behavior in normal state and samples which have lower resistivity showed higher critical current density. The resistivity just above onset temperature decreased with increasing the calcining temperature up to 950 °C, but above 975 °C the opposite behavior was observed. This behavior was discussed in connection with x‐ray diffraction patterns of the samples.