Metallurgical studies and optimization of sintering condition to obtain the maximum volume fraction of the highTcphase (∼110 K) have been made for the Bi‐Sr‐Ca‐Cu‐O system. In the differential thermal analysis, double peaks of endothermic reaction at ∼870 and ∼910 °C were observed during the increase of temperature, and a weight loss accompanied each endothermic reaction. Optimum calcining and sintering conditions to obtain a large volume fraction of the highTcphase were 820 °C×14 h+840 °C×6 h and 875 °C×100 to 200 h in air, respectively. As for the variation of Cu concentration, nominal composition of Bi1Sr1Ca1Cu2Oxgave the maximum volume fraction of the highTcphase. (For these specimens, sintering time was varied up to 20 days.) Post annealing at 400 °C for 20 h in an oxygen atmosphere after the sintering at 875 °C for 100 to 470 h in air had little effect on the improvement of volume fraction of the highTcphase. As for the specimen to which Pb is added, however, the post annealing at 400 °C for 20 h increased the volume fraction of the highTcphase. Scanning electron microscopy showed that the Bi1Sr1Ca1Cu2Ox(nominal composition) specimens sintered at 875 °C for 100 to 470 h consist mostly of well‐grown thin layers, while the specimen sintered at 875 °C for 14 h consists mostly of fine pieces of thin layers piling up at random. Electron probe microanalysis revealed that microstructure of the specimen sintered at 875 °C consists of Bi‐poor regions and the matrix surrounding them, and that these Bi‐poor regions are classified into Cu‐rich regions and Ca‐rich regions. The superconducting phases of this material are considered to exist in the matrix region. We identified the Cu‐rich regions and Ca‐rich regions as (Sr0.45, Ca0.55)3Cu5Oxand (Sr0.08, Ca0.92)2CuOx, respectively. The average size of these regions increased with increasing time of sintering, although total volume fraction of these regions did not increase.