Al2O3-Si composite specimens were prepared using fused corundum, ultra-fine α-Al2O3 and Si powder as starting materials and resin as binder. Effects of sintering atmospheres on properties, phase composition and microstructure of specimens after firing at 1 500 ℃ were investigated. The results show that: (1) after firing in oxidizing or weak oxidizing atmosphere, there is some Si in the specimens and some glass phases containing mullite form on specimen surface, the density and strength at room temperature are relatively high, but hot modulus of rupture and thermal shock resistance are relatively poor; (2) after firing in weak reducing or reducing atmosphere, Si reacts completely with CO or N2 forming whisker-like SiC, granular Si2N2O or O’-SiAlON, and the thermo-mechanical properties of specimens are enhanced; (3) after firing in nitrogen atmosphere, Si reacts completely with N2, CO or C forming whisker-like SiC and columnar β-SiAlON crystals, the hot modulus of rupture and thermal shock resistance of specimens are enhanced noticeably.