The La xY 1- xBa 2Cu 3O 7-δ (0< x<1.0) system of superconductors has been investigated for the variation of structure and superconducting properties. It has been found that for x⩽0.5 the system behaves more like a pure Y 123 superconducting oxide with Tc (onset) ≈90 K. We obtained a maximum Tc=94 K (zero resistance at 91 K) when x=0.1. For x>0.5, the system starts behaving like a La 123 system with a high sensitivity of superconducting and semiconducting properties to heat treatment and oxygen content. The solid solution oxides are shown to exhibit semiconducting, metallic or superconducting behavior with increasing oxygen content. Two different preparative techniques have been used to obtain superconducting solid solution oxides. Two parameters, the orthorhombic structure and the oxygen content, have been identified to primarily influence the superconductivity of the (La xY 1- x) 123 oxide. Based on the observations of orthorhombic and semiconducting (La xY 1- x ) 123 samples, it has been suggested that these two parameters independently influence the properties of the (La xY 1- x) 123 oxide for x>0 and both are essential for the superconductivity of these oxides. Our study supports the idea that the exchange of La with Ba in the ideal perovskite A site is a main contributor to the variation of the superconducting properties. Oxygen incorporation in the O(4) site and the randomization of the O(1) and O(5) sites are believed to result in a more symmetric tetragonal structure leading to disruption of the two dimensional Cu-O network, considered essential for the superconductivity of the 123 system.