Gas-sensitive layers of iron oxide microparticles have been obtained by nebulization of iron oxalate solution, size-selective deposition of the dried aerosol particles and final heating at 350-degrees-C to transform the oxalate to iron oxide. Clustered layers of spherical particles with a size of about 800 nm resulted. For comparison sputtered iron films were oxidized at the same temperature to yield oxide films of compact morphology. With secondary-neutral and secondary-ion mass spectrometry film thicknesses, elemental compositions and chemical states were measured. All prepared iron oxides were determined to be primarily Fe2O3. The granular as well as the compact iron oxide films were investigated concerning their change in electrical conductivity upon exposure with organic gases contained in air. The sensitivities at 350-degrees-C for propane and methane, but not for benzene, were found to be higher for the granular films. The response times were not much different between the particulate and the compact iron oxide layers.