ZnS and La-doped ZnS thin films were successfully synthesized by using chemical bath deposition on conductive glass substrates. The effects of La doping on the surface morphology of the films were investigated with SEM, and the deposition process of ZnS thin films was analyzed with CHI660B electrochemical comprehensive analysis. The prepared ZnS thin films were nearly spherical and compact. The electrode potential shifted negatively, deposition rate decreased and the particle size increased with La doping into the ZnS films due to the adsorption of low electronegative La on the electrode surface. It is suggested that electrochemical investigation is an effective tool in studying ZnS deposition process by chemical bath deposition.