Growth of magnetic iron oxide thin films by a chemical vapor deposition process from metallorganic iron acetyl acetonate precursor under atmospheric Ar-O-2 transport is described. Kinetics of film growth depends on deposition parameters, particularly substrate temperature, gas flow rate, and location of substrate away from the source which is a direct effect of mass transfer and pyrolyzing efficiency of precursor vapor. As-deposited films essentially have alpha-Fe2O3 phase which is transformed by a sequential reduction-oxidation process into Fe3O4 and gamma-Fe2O3 phases as revealed by electron diffraction studies. The modification in the crystalline phase of the as-deposited film is observed by varying the substrate orientation and Ar to O-2 gas-phase ratios. The gamma-Fe2O3 phase of iron oxide films in the as deposited form, is realized by using pure Ar as transport gas. Microstructural changes as well as magnetic properties of iron oxide thin films on transformation into different polymorphic crystallographic phases are described.