Si₃N₄ ceramics used in this study were introduced to oxygen during preparation by three different methods; (1) pre-oxidation of raw powder, (2) sintering in different atmospheres, (3) controlling the amount of Al₂O₃ to be added as a sintering additive. Their oxidation behavior in term of change in mass, morphology surface composition and cross-section of the specimen, was studied between temperature of 1200 and 1400°C Though mass change could hardly be seen below 1300°C, it was observed remarkably at 1400°C. In isothermal oxidation at 1400°C, as the amount of Al₂O₃ increases from 2mass% to 4mass%, the mass of the specimen also increases. However, the effect of pre-oxidation of raw powder and sintering in different atmospheres does not appear on oxidation resistant Si₃N₄ ceramics. Oxidized layers were formed on the surface of the specimen and they consist of two or three layers. Those specimens which had lower Al and O atom solid solution was superior to higher solution specimens, because lower solid solution specimens have greater hardness and strength. As a result, it was considered preferable that Al and O atom solid solution should be lower in the range of sinterability accerelation.