Cadmium selenide (CdSe) thin films have been prepared by chemical bath deposition on glass substrates in chemical solution and the pH controlling agent has been altered. The band gap energy of CdSe thin films was determined by using UV–visible spectra. The structural and surface morphological properties were studied by X-ray diffraction and scanning electron microscopy. Furthermore, Rutherford backscattering spectroscopy, as a powerful technique in surface science, was used to investigate the stoichiometry and the variation of the depth profile concentration of Cd and Se elements along the thickness of the prepared samples. The result indicated that the pH has a crucial role in physical properties of prepared CdSe thin film and can control the procedure of deposition to achieve the desired value of band gap energy, quality of crystallity and homogeneity of the prepared thin films.