ABSTRACTPhases and their relations in the Bi, Pb–Sr–Ca–Cu–O system have been studied to afford a sound material scientific base. Of particular interest is the chemically most representative system, Bi–Sr–Cu–O, in which a series of solid solutions expressed as Bi2+xSr2−xCu1+yOz are formed. The superconductor (Tc≃10K) corresponds to an extremely narrow range of 0.1<x<0.13. From the composition dependence of the one-dimensional modulation mode a new important factor controlling the modulation mode has been deduced. Substitution of Pb for Bi in the high-Tc phase has been found to induce a stepwise change of the modulation mode, thus suggesting an ordering of Pb in the BiO layer. [CuO2]∞ planes exist both in the holeand electron-carrier superconductors, but their role in the former type of superconductors has not been known. As one possible contribution to attacking this problem, ACuO2 (A: Ba1/3Sr2/3˜Sr˜Ca2/3Sr1/3 ) crystallizing in /A/CuO2/A/CuO2/A/ structure have been prepared using high pressures of 60kb.