In order to prepare berthollide type of iron oxide (i.e., nonstoichiometric magnetite; FeOx:1.34<×<1.5) thin films, iron targets were sputtered in pure water vapor at the pressure of 2×10−3Torr by using a high rate sputtering apparatus with faced targets. The composition and crystal structure of the obtained films strongly depend on input power Ptand substrate temperature T2. The increase of Ptand Tslead to the reduction of oxygen content in the films. The films deposited at Ptabove 300 W and Tsof 200 °C exhibit a spinel type of crystal structure. Their lattice constant a0and resistivity &rgr; change monotonically from a0and &rgr; for &ggr;‐Fe2O3to those for Fe3O4with an increase of Ptfrom 300 to 800 W. On the other hand, when Ptis kept constant at 300 W, berthollide type of iron oxide films was deposited at Tsof 220–270 °C. The optical spectra of glow discharge reveal the existence of a large amount of ionic species such as H+and OH+in the space between targets. They seem to be effective for the formation of the berthollide type of iron oxide.