Oxygen gas sputtering was carried out on cellophane sheets. The surface was vigorously etched and a characteristic microstructure was developed. At the early stage of sputtering numerous small and shallow projections or microcraters sized about 0.1μm were homogeously developed over the entire surface. The projections changed to tatterly cones and their size increased with the sputtering energy on sputtering at a mild gas pressure. The size of the cones also increased with a decrease of electric power. Apparent etched depth for oxygen gas sputtering was about two times bigger than that fo argon gas sputtering at any sputtering energy. The appearance of bigger tattery cones at a high sputtering energy and a low electric power caused a marked increase in opacity of the cellophane sheet. The cone size and the distace between cones were analysed using a run-length analysis of the black and white part in digitized scanning electron microscopic images of the microstructure on the surface. The most contributory run-length to opacity increase was 0.5μm.