The oxidation behavior of Ca-alpha-Sialon composites prepared by using the powders of alpha-Si3N4, AIN, Al2O3 and CaCO3 as the starting materials has been studied, for the composition Ca0.8Si8.8Al3.2O16N14.4 in the temperature range of 1200 to 1400 degrees C for 24 to 96h in an air stream. The bending strength and weight gain of the samples before and after oxidation experiment were measured, and the phases of surfaces of the samples were examined by XRD, the microstructures of sections and surfaces of the samples were observed by SEM. The results show that the weight gain increased and the bending strength decreased as the oxidation time increased, and the oxidation layers contained bar cristobalite and glass phase at 1200 degrees C, bubbles and glass phase at 1300 degrees C, transparent glassy film and the pores at 1400 degrees C, the phases of oxidation layers consisted of cristobalite, CaAl2Si2O8, and glass phase.