Since the discovery of high-Tc superconductivity in the La-Ba-Cu-O system, many kinds of oxide-superconductors have been found out: the 40K-superconductor La_2-xA_xCuO₄ (A = Ca, Sr and Ba), the 90K-superconductor RBa₂Cu₃O_7-y (R = Y and most of the lanthanide elements) and newly discovered Bi- and Ti-oxide systems. These compounds, together with BaPb_1-xBi_xO₃ of Tc = 12K, are based on the perovskite-related structure. The present paper reviews common structural features in these oxide-superconductors.