During the 13th Japanese Antarctic Research Expedition in 1972-1973 the determination of the carbon dioxide content of the surface air was carried out at Syowa Station (69°S, 39.5°E) in Antarctica, by using Infra-Red Gas Analyzer. The station is located on East Ongul Island, 5km off the Antarctic Continent, and the elevation of the laboratory is about 13 m above sea level. The mean value of the carbon dioxide content of the dry surface air was 322±7 ppm during the period from March 1972 to January 1973. Some of the seasonal variations observed were as follows: 1) The carbon dioxide content showed high values in the Antarctic summer season (324±4 ppm). 2) At the end of the Antarctic summer, the content decreased abruptly. 3) Low values were observed in early winter-May, June and July (319±4 ppm). 4) Gradual increase was observed late winter-August, September, October and November (319±4 ppm → 323±3 ppm). 5) The mean value for 11 months was 322±7 ppm. The annual variation pattern of the carbon dioxide content at Syowa Station showed a slight difference from the results obtained by PALES and KEELING (J. Geophys. Res., 70, 6053, 1965) at Hawaii and by BROWN and KEELING (J. Geophys. Res., 70, 6077, 1965) at the South Pole.