Spin coated sensor films of nano-SnO2 with bimodal nano-size particle distribution were obtained through thermal decomposition of SnCl2 using a simple and fast single step thermal decomposition technique. The deposition was done on soda-lime glass substrates using variable decomposition/firing temperature in the range of 400-600 degrees C at the interval of 50 degrees C. The effect of firing temperature on structural, micro-structural and optical properties was studied by X-ray diffractometer (XRD), atomic force microscopy (AFM) and UV-Vis respectively. AFM study of the films revealed a special type of microstructure i.e. conducting larger globules of 8-20 nm with smaller nanoparticles of <= 3 nm on the surface of the bigger globules. The films fired at 400 degrees C exhibit the highest UV absorption peak compared to other samples. A highest response (R-air/R-gas = 24) to 300 ppm of H-2 is recorded for films fired at 550 degrees C and they exhibit sensitivity of similar to 90 x 10(-3) for concentration of H-2 (1-20 ppm). These sensors also exhibit good stability of resistance at the optimized operating temperature of 265 degrees C and in the presence of different relative humidity (RH 20 - 100%). (C) 2012 Elsevier B.V. All rights reserved.