Polycrystalline CdS films of good quality could be obtained by electrolysis with rectangular voltages on indium tin oxide/glass substrates from low concentration of CdSO4 and Na2S2O3 in aqueous solution system of pH 3.1 at room temperature (r). The films obtained during 6 s at - 1.0 V (versus Ag /AgCl/ 3 M NaCl) and 6 s at 0.0 V gave stoichiometric CdS with a hexagonal polycrystalline structure with a preferred a-axis orientation. It is suggested that the mass transfer of Cd2+ to the substrate surface governs the deposition rate of CdS. The film deposited at 6 s of - 1.2 V and 6 s of 0.0 V gave a c-axis preferred orientation. Incorporation of S into the films was affected by the applied potential, and the reduction of S controls the deposition reaction.