The powder mixture of Si3N4-AlN-Y2O3, Si3N4-AlN-CeO2 and Si3N4-AlN-Y2O3-CeO2 system was hot-pressed at 175$0^{circ}C$ for 2h in N2 to prepare $alpha$-Sialon ceramics. The mechanical property and oxidation behaviour of the prepared $alpha$-Sialon ceramics were investigated. At 120$0^{circ}C$, oxidation resistance was best for the Y2O3 added $alpha$-Sialon ceramics and oxidation rate increased when the amount of CeO2 increased. But when the mixture of Y2O3 and CeO2 added $alpha$-Sialon ceramics showed a good oxidation resistance. Fracture toughness of (Y2O3＋CeO2) added $alpha$-Sialon ceramics was higher than Y2O3 added $alpha$-Sialon ceramics.