The present paper a SnO2 (Pure) and Ag doped thin films at different concentration (3, 5 and 7 vol.%) of Ag, were prepared by chemical spray pyrolysis. The films deposited onto glass slides were first cleaned with detergent water and then dipped in acetone and discusses the structural, optical and sensitive properties of Ag-doped tin oxide thin film prepared on glass substrate by the spray pyrolysis technique at a temperature of 400 ̊C. X-ray diffraction study shows that the film was tetragonal rutile structure of SnO2. Morphology analysis studied by atomic force microscopy (AFM) and reveals that the grain size of the prepared thin film is approximately (73.41-111.62) nm, with a surface roughness of (2.18 – 2.79) nm as well as root mean square of (2.69 -3.39) nm for SnO2(pure)and Ag-doping, Optical characteristics were studied by UV/VIS Spectrophotometer at (300- 1100 nm) and observed that the transmission value was more than 75 % at the visible wavelength range. The direct energy gap (Eg) ranged between (2.73-3.22) eV, is measured by UV/VIS., and studied the sensor properties t0 NO2 gas with 3% ratio at a constant voltage of 6V, to found the optimum operation temperature at 150°C for all films, also the sensor work in room temperature. The sensitivity increases with temperature to arrive (81.6%) for SnO2: Ag films at 250°C. The response time was (5.4sec) and the recovery time was (27sec) for SnO2: Ag gas sensor. The results obtained that SnO2 film prepared by chemical spray pyrolysis pure and doped by Ag were a good sensitive for NO2 gas.