Cu-doped CdS thin film has been successfully deposited by ion-beam sputtering deposition. The structural, morphology, optical and electrical properties of as-deposited and annealed Cu-doped CdS thin films were investigated. The heavily Cu-doped CdS films annealed at 400 degrees C was demonstrated to be improved in structural, morphology, electrical and optical properties. X-ray diffraction (XRD) analysis indicated the formation of polycrystalline CdS film with the structure of hexagonal wurtzite phase. No distinct impurity of Cu and Cu-S phase was detected in Cu-doped CdS thin films Atomic force microscopy (AFM) revealed that the grain. size was increased after annealed. Optical transmission and absorption spectroscopy measurement revealed a high absorption and energy band gap was of about 2.40 eV. The CdS thin film was of p-type conductivity and the resistivity was found to be 1.28 x 10(-1)Omega cm.