SiO 2 films were prepared by an ion-beam sputtering (IBS) method and their properties were studied using visible-UV absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) and IR transmission spectroscopy. The SiO 2 films prepared with O 2 atmosphere had good transparency in the visible region. Only the XPS signal due to the Si-O 2 bond was observed, and the film composition was almost stoichiometric. However, the full widths at half maximum of the XPS peak and each IR band of the SiO 2 films were larger than those of thermally oxidized SiO 2 films. This suggests that the SiO 2 films prepared by the IBS were more disordered than the thermally oxidized SiO 2 films. The IR spectra showed that the structure of the SiO 2 films prepared by the IBS method was mainly coesite like and was different from that of the thermally oxidized SiO 2 which was mainly quartz like.