Virgin and Sm-doped CdS thin films were prepared by spray pyrolysis route on glass substrates. The influences of Sm-doping amount on structural, topographical, optical and electrical properties were examined. It was found from X-ray diffraction data that virgin and 1 and 2 at.% Sm-doped CdS samples grew along (002) plane whereas the preferred orientation changed to (101) starting from Sm doping of 3 at.%. Morphological investigation showed that even though CdS specimen had irregular shaped grains, Sm-doping substantially modified the surface topography of CdS thin films. A maximum transmittance were attained for 4 at.% Sm-doped CdS sample. After Sm-doping, a slight increase was observed in the band gap value of CdS thin films. It was found from the room temperature photoluminescence data that compared to the virgin CdS, the intrinsic defect population of Sm-doped CdS thin films reduced, meaning that more stoichiometric films formed. From the electrical measurements, it was determined that 1 at.% Sm-doped CdS thin films exhibited the best electrical properties, i.e., maximum carrier density and minimum resistivity. Based on all the data, it could be pronounced that 4 at.% Sm-doped CdS displayed the best optical properties, whereas the optimum electrical characteristics were reached for 1 at.% Sm-doped CdS thin films.