In the present work the structural effects of La2CuO4 doping with CeO2, or of supporting the former on the latter, have been investigated. It was found that lanthanum oxide possesses a very good solubility in cerium dioxide in the presence of copper oxide, forming a solid solution. According to our experimental data, at 1050 degrees C and in the presence of copper oxide (over 1.5% mass), the boundary for the existence of the Ce1-zLazO2-z/2-delta phase falls between z = 0.398 and z = 0.462. Copper oxide itself has a very low, but appreciable solubility in this system. The excess of CuO strongly increases the rate of formation of the solid oxides solution, due to its relatively low melting point.