Mn-dopant concentrations ranging from 0.05 mM to 10 mM were utilized for producing Mn-doped CdO thin films on glass substrates employing spray pyrolysis technique. The structural, morphological, topological, optical, and vapour sensing properties of CdO thin films are acknowledged to be impacted by Mn doping. According to the XRD analysis, the generated thin film displays polycrystalline nature with a cubic structure and Mn doping also contributes to a substantial reduction in the crystallinity of CdO thin films. SEM images show homogenous grains, and as the concentration of dopants rises, so does the size of the aggregated grains. The absorbance and transmittance spectra of the produced thin films captured in the UV visible spectra demonstrate that the transmittance of the CdO thin film has decreased substantially with an increase in Mn dopant concentration along with a significant red shift with respect to molar concentration which may facilitate a good sensing behaviour of the test sample. The findings indicate that the band gap energy decreases with doping concentration, ranging from 2.85 to 2.59 eV. The intensity of the SAED pattern has significantly decreased, implying that the doped samples' degree of crystalline nature has decreased. According to the photoluminescence spectra, the emission band near 485 nm is produced by both the pure and doped CdO nanoparticles. The ethanol sensing behaviour of the prepared thin film was examined using the chemiresistive method at room temperature. The film's responsiveness to vapour drastically increased with an increase in Mn dopant concentration, leading to the development of a thin film that is incredibly selective for ethanol vapour. Based on the findings of this study, room temperature ethanol sensors can be developed by making use of Mn-doped CdO thin films.