Oxidized indium thin films on several substrates were formed by indium deposition and thermal oxidation. The oxidation was carried out in oxygen ambient at temperatures ranging from 500 to 900 degrees C for 1 h. In the scanning electron microscopy measurements, the oxidized indium films were shown to be composed of grains with sizes of 400 to 600 nm which agglomerate subgrains with diameters of 40-60 nm. From the measurements of X-ray diffraction, X-ray photoelectron spectroscopy and Auger electron spectroscopy, it was confirmed that the oxidized indium are cubic indium oxide (In2O3) polycrystallites. In addition, no elements other than In and O atoms were found from secondary ion mass spectroscopy measurements. A strong orange photoluminescence, peaking at 637 nn, was observed at room temperature for these films. It was assumed that a center of orange luminescence in the indium oxide films may be related to oxygen deficiencies or defects.