Chemical spray pyrolysis-grown CdS thin films including various quantities of Eu atoms (from 0 to 10 at.%) were synthesized on glass slides. The detailed physical properties of the produced CdS and CdS:Eu thin films were explored. Structural analysis showed that Eu-doping enhanced the crystal quality of CdS thin films until 10 at.% Eu-doping and further Eu-doping treatment led to a distortion in the CdS structure. In addition, the crystallite sizes of CdS thin films dropped from 36.2 to 32.4 nm as Eu-doping level increased to 10 at.%. Morphological data showed that increasing Eu-doping remarkably varied the surface morphology of CdS thin films forming smaller grains. Chemical content examinations approved the presence of Eu atoms in CdS structure. From the optical measurements, it was obtained that more transparent CdS thin films with a maximum transmittance of 68% at 820 nm were created after 10 at.% Eu-doping and bandgap values of samples reduced from 2.58 to 2.47 eV with rising of Eu-doping from 0 to 10 at.%. Room temperature photoluminescence data demonstrated the formation of two essential peaks for all the samples, which are in turn related to green and yellow bands. Electrical investigation pointed out that Eu-doping enhanced the carrier density of CdS thin films from 4.38 × 10¹³ cm^− 3 to 2.46 × 10¹⁴ cm^− 3 and dropped the resistivity of CdS samples from 2.59 × 10⁴ Ω cm to 5.85 × 10³ Ω cm until 6 at.% and further increment of Eu-doping paved the way to get worse electrical data. Thus, it can be brought a conclusion that Eu-doping not only improved the optical properties of CdS thin films, but also restored the electrical properties, which are able to use in the opto-electronic devices.