After the discovery of YBa2Cu3O7-y with an unusually high superconducting transition temperature (Tc), around 95 K , similar compounds were made by completely replacing Y by the other rare-earth elements. It was found that RBa2Cu3O7-y (RBCO; R = rare-earth) possessed the same orthorhombically distorted layered perovskite structure and virtually the same Tc for almost all R [2–8]. The exceptions are compounds with R = Ce, Pr and Tb. The stable tetravalent state of these three R elements, as contrasted with the stable trivalent state of the other R elements, may be the reason behind this problem . But there are also problems in producing single-phase, high Tc samples with La, Yb and Lu substitutes [10–12]. One of the reasons for this may be the size of these R ions: the difference between their radii and that of Y3+ is comparably large. Here we present the results of our systematic study of the structure and transport properties of the series of compounds La1−xYbxBCO (0.05 ≤ × ≤ 0.95).