Direct aerosol sampling of Antarctic aerosols was carried out in the free troposphere over Syowa (39.58¿E, 69.00¿S) and Mizuho (44.19¿E, 70.41¿S) stations in April and December 2000 for better understanding of aerosol constituents and their vertical distribution in the Antarctic troposphere. Individual aerosol particles were analyzed/observed by means of a transmission electron microscope and a scanning electron microscope equipped with an energy dispersive X-ray spectrometer. Aerosol particles containing sulfur species (probably H2SO4) were identified as the major aerosol particles in the Antarctic free troposphere, whereas sea-salt, mineral and anthropogenic particles were minor aerosol particles. Although H2SO4 and sea-salt particles were observed in the free troposphere during both April and December, mineral and anthropogenic particles were distributed only in December. Sea-salt particles show lower Cl/Na molar ratios relative to seawater because of Cl liberation. S/Na molar ratios of the particles are also low, suggesting that Cl- in the sea salt had been replaced by anions other than SO42- and CH3SO3-. The Cl liberation from sea-salt particles in the Antarctic free troposphere might have occurred via the heterogeneous reactions mainly involving reactive nitrogen oxides.