In the present investigation, a low-cost and high-operational sol-gel spin coating technique for preparing undoped and various Europium (Er)-doped CdO films of molar percentages of 1%, 5%, 10%, and 15% were considered. Using X-ray diffraction, the polycrystalline nature reveals two preferred orientations of (111) and (200). The mean crystallite size was evaluated and increased from 20.95 to 49.37 nm using the well-known Scherer’s formula by increasing the Eu- dopant content. The atomic force microscopy images indicate a homogeneity of a granular distribution deteriorated with Eu-content. The root means square roughness value was evaluated and increased from 4.1 nm to 284 nm with Eu-doping. High transmission of approximately 80% in the visible region spectrum was recorded. The optical band gaps are increased from 2.2 to 2.46 eV from the undoped and various Eu-content %. A relationship between the Eu- content % for CdO films and the optical parameters was discussed to support the availability of the device for optoelectronic applications.