This paper describes the anodization of germanium in an oxygen-plasma excited by a high-frequency electromagnetic field. The refractive index of the plasma-anodized GeO2 film is about 1. 66. The transmittance of the oxide film on Ge was measured on an IR-450S type infrared spectrophotometer. The experiments show that infrared absorption bands of the GeO2 film are at 870cm-1 and 560 cm-1. The stretching constant of the Ge-O bond α (439N/m) and the Ge-O-Ge bond angle θ(129°) were calculated from the infrared were calculated from the infrared absorption data together with the edges of vibration bands predicted by the center-force-network model of Sen and Thorpe.