Chemical compositions of superconductors of Bi1−xPbxSrCaCu1.8Oy (x = 0.1, 0.3, and 0.5) were investigated by analytical electron microscopy (AEM) supplemented by electron microprobe analysis. Samples were prepared by a solid state reaction method under oxygen partial pressures of 0.20 and 0.077 atm. The high-Tc phase appeared only in the samples of Bi1−xPbxSrCaCu1.8Oy (x = 0.1 and 0.3) prepared under an oxygen partial pressure of 0.077 atm. In the samples containing the high-Tc phase, stacking structures of 2, 3, and 4 perovskite layers were observed by transmission electron microscopy (TEM). From AEM analysis, it was shown that in order to make the high-Tc phase, the substitution ratio of Pb for Bi was about 0.2.