Polycrystalline SnO thin films were prepared at 600°C by metal organic chemical vapor deposition (MOCVD) technique using tetraethyltin as an organometallic (OM) source and UHP O as oxidant. The films were analyzed by means of XRD, SEM, and AES for their microstructure characterization and subjected to H and CO gas detection. The results were compared to SnO 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% H 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.