The most important details of the synthesis by using pulsed laser ablation in deionized water to ablate the Cr2O3 and TiO2 nanoparticles and drop-casting the solutions on the substrates to deposit Cr2O3 thin films with concentration ratio (0 , 0.2 , 0.4 , 0.6 , 0.8)% of TiO2 are illustrated. Additionally, a concise and precis explanation of the structural analysis included X-ray diffraction (XRD) and atomic force microscopy (AFM) and gas sensor performance evaluation were provided. (XRD) test revealed that all samples of Cr2O3: TiO2 films have a polycrystalline nature with Rhombohedral structure and the Cr2O3 is crystalized as a main plane in (012),while TiO2 nanoparticles have anatase phase with tetragonal crystal structure at plane (112). The gas sensor device of the heterojunction of Cr2O3: TiO2/Psi with concentration ratio (0 , 0.2 , 0.4 , 0.6 , 0.8)% of TiO2 were examined when exposed to 400ppm of NO2 gas at various temperatures (R.T , 100 , 150)°C. The maximum value of sensitivity was 475.11% detected at 0.6% TiO2 at operation temperature of 100°C.