Nickel oxide (NiO) sensor films were prepared on glass substrate by a sol–gel spin coating technique. These films were characterized for their structural and morphological properties by means of X-ray diffraction, field emission scanning microscopy and atomic force microscopy. The NiO films are oriented along (200) plane with the cubic crystal structure. These films were utilized in nitrogen dioxide gas (NO₂) sensor. The dependence of the NO₂ response on operating temperature, NO₂ concentration was investigated. The NiO film showed selectivity for NO₂ over Cl₂ compared to H₂S (S_NO2/ S_Cl2 = 37:5; S_NO2/S_H2S= 3.4). The maximum NO₂ response of 23.3 % with 85 % stability at gas concentration of 200 ppm at 200°C was achieved. The response time of 20 s and recovery time of 498 s was also recorded with same operating parameters.