Abstract: Sialon-corundum multiphase refractories were synthesized once through using silicon powder, aluminum powder and black corundum as raw materials. Effects of Si3N4/AlN additives on N content, modulus of rupture and microstructure of Sialon were investigated. The results showed that the N content in the synthesized material increase and its flexural strength increases then decreases along with the increasing Si3N4/AlN content. N content in the specimen approaches to saturation after nitriding at 1330°C for over 8 hours. The additive may lower greatly the synthesizing temperature of the Sialon phase. In the synthesis process the range from 1230°C to 1280°C is an important initial nitriding phase in which the whole nitriding reaction can be completed by 94.2%. It was proved that nitriding fully Al and Si in early stage is beneficial to the formation and complete grain growth of Sialon phase.