Cadmium oxide (CdO) thin film was optimized on glass substrate at 250 °C using a chemical spray pyrolysis (CSP) technique followed by Al atoms doped into it with various wt% in order to study its influence on structural, electrical, optical, morphological and gas adsorption properties of the CdO thin films. All the films are deposited in polycrystalline cubic crystal phase is confirmed by XRD. The 90% of the visible as well as near infrared (650–850 nm) region energies is transmitted in pure and Al doped CdO films. Smooth surfaces and spherical shaped nanoparticles morphologies are conspicuous in CdO films after Al doping. The prepared CdO film is of n-type conductivity with having mobility of 64.4 cm² V^-1s^-1 and carrier concentrations of 2.2 ×10²⁰ cm^-3. Importantly, the mobility increases and resistivity decreases is observed on CdO film as for Al doping level. After procuring some interesting physicochemical properties in CdO films by Al doping, trimethylamine (TMA) gas sensing analysis has been scrutinized using a simple and cost effective route. Finally, it is found that low resistive and high mobility of 1.5% Al doped CdO film exhibited pronounced sensitivity, 32.12%, is due to its higher specific surface area and as well as existence of more defective sites.