Cadmium sulfide thin films are prepared on glass substrates at 82 degrees C for 1 hour by chemical bath deposition. After deposition, the films are annealed at 480 degrees C for 1 hour in air atmosphere. Both as-grown and annealed films are characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, optical absorption spectroscopy and current voltage characteristics and their structural, morphological, compositional, optical and electrical properties are investigated. The X-ray diffraction patterns of deposited films show the formation of polycrystalline of CdS with both cubic and hexagonal structure. Moreover, after the thermal treatment of 480 degrees C, they mostly turn into polycrystalline CdO with cubic structure. The grain size of the deposited film decreases approximately from 10-20 nm to 2-3.5-5.5 nm by annealing. The band gap energy of the films is determined for the direct transitions of 2.15 eV and increased to 2.25 eV by the thermal treatment. After thermal process, the electrical conductivity of the films calculated from the current-voltage characteristic in the dark increases from 5.482x10(-10) (Omega cm)(-1) to 5.304 x 10(-8) (Omega cm)(-1). The observed conduction mechanism in both as-grown and annealed films is ohmic.