Polycrystalline SnO2 thin films were prepared at 600°C by metal organic chemical vapor deposition (MOCVD) technique using tetraethyltin as an organometallic (OM) source and UHP O2 as oxidant. The films were analyzed by means of XRD, SEM, and AES for their microstructure characterization and subjected to H2 and CO gas detection. The results were compared to SnO2 thick-films derived from metal organic decomposition (MOD) in order to study differences in gas sensing characteristics in relation to the microstructure. The microstructure of the MOCVD-derived thin films was fully dense columnar structure with rough surface morphology while that of the MOD-derived thick films was porous structure resulting from loosely interconnected small crystallites. Both types of sensors showed good reproducibility and stability toward 1% H2 gas with an enhancement of the sensitivity and the time response in the thick-film sensor. The sensing characteristics were degraded under 1% CO gas for both types of films.