The crystal structure of phases, microstructure, and elemental composition of Y2O3-doped gamma-AlON were characterized by the analysis of XRD, FESEM, and EDS, and the oxidation behavior was studied by the oxidation tests and TG-DSC analysis in air from room temperature to 1300 A degrees C. TG-DSC results show that the oxidation weight gain changes from 10 to 2 % and the vigorous oxidation temperature of gamma-AlON changes from 1100 to 1200 A degrees C after doping with 2 wt% Y2O3. Y3Al5O12 (YAG) phase and AlYO3 (YAP) phase were formed as second phases in Y2O3-doped gamma-AlON ceramic due to the reaction of Y2O3 with Al2O3. Y2O3-doped gamma-AlON ceramic exhibited denser microstructure as compared to gamma-AlON ceramic. The relationship of oxidation weight gain with oxidation time follows a parabolic law. The oxidation reaction rate of Y2O3-doped gamma-AlON is far less than that of pure gamma-AlON. YAG and YAP distributing at the grain boundaries and the higher relative density contribute to the improvement in the oxidation resistance of Y2O3-doped gamma-AlON.