Under the Synthesis of Nanocrystalline Metal Oxides for Gas Sensors activity, nanocrystalline / mesoporous tin oxide powders were prepared using chemical techniques. The gas sensitivity of the derived sensors were investigated for various gases ethanol, acetone, TMA, DMA, ammonia, NOx, CO, LPG and CNG. SnO2 powder was prepared by precipitation route. Ammonia and NOx sensors are desired for environmental monitoring and food freshness monitoring. A systematic study was made to improve ammonia and NOx sensitivity using doped (Pt, Au, Pd) WO3 as sensitive material. The effect of overlayers such as SiO2, on response time and gas sensitivity was investigated in detail. A project on Nanostructured metal oxide gas sensor array for detection of chemical warfare agents, was sanctioned by DRDO.