Recently, there has been an increasing demand for thin film solar cells due to the decrease of primary energy sources. The materials which are used in these devices need to be produced by low cost production techniques and possess improved characteristics. CdS is a well-known material for thin film solar cell applications. We have tried to investigate the effect of Cu doping (1, 3 and 5 at %) to CdS. Undoped and doped CdS films have been obtained by ultrasonic spray pyrolysis (USP) technique which is economic and simple to process. The structural, surface and optical properties of the films have been investigated. X-ray diffraction has been used to analyze the structural properties. Morphological properties have been investigated by scanning electron microscopy (SEM). Energy dispersive x-ray spectroscopy (EDX) has been used to perform elemental analysis. The optical parameters have been analyzed by a UV spectrometer.