The effect of ppm level Ha on the d.c. resistance of SnO2 thick film planar resistor with SnO2 particle size variation (similar to 20 to 50 nm) is reported. SnO2 nanoparticles were synthesized using the sol-gel method. The films were prepared using standard screen printing technology. The SnO2 crystallite size, D, is varied in the range of 20-50 nm and sensitivity for H-2 is found to increase steeply as D decreases.