We have prepared (ZnO)(x)(CdO)(1-x) thin films by spray pyrolysis. Mixed thin film oxides with different compositions of cadmium and zinc were deposited on glass substrates and exposed to different annealing treatments at a fixed temperature. The effects due to post-thermal annealing on the structural, optical and electrical properties of the variable composition thin films have been studied depending upon the x value. The crystalline structure was studied by X-ray diffraction (XRD). We found the presence of CdO XRD patterns for low Zn concentrations, and a mixing of CdO (cubic) and ZnO (hexagonal) phases for low Cd concentrations. In all cases. the crystallite sizes increased with the annealing. In addition, the band-gap and the resistivity vary between those found for pure CdO and ZnO. The changes of the latter parameters with the post-thermal annealing are studied also as a function of the x value.