Thin films of pure nano-crystalline SnO2 and WO3-doped SnO2 in different concentrations (3 wt.% and 5 wt.%) are deposited using sol-gel spin coating technique on glass substrates. The structural and morphological properties of these films are investigated using XRD, TEM and AFM. The sensitivity and selectivity of these films are tested to different reducing and oxidizing gases such as SO2, NH3, NO2 and ethanol. A SnO2 thin film with 5 wt.% WO3 shows very high responses to NO2 (four orders of magnitude in the value of (Rg - Ra)/Ra; Rg and Ra are the resistance in NO2 and in air, respectively) and excellent selectivity for NO2 gas at a low operating temperature of 150 °C. The effect of WO3 on the sensing characteristics of these films towards NO2 is discussed. © 2006 Elsevier B.V. All rights reserved.