Fine beta-sialon (Si6-zAlzOzN8-z, 1 < z < 4) was prepared by mechanical-activated combustion synthesis (CS) using raw materials such as Si, Al, and SiO2 in a nitriding atmosphere of 1 MPa. Mechanical activation by planetary milling for only 18 min led to the formation of beta-sialon after combustion synthesis. Comparative experiments with ball milling showed that the relative amount of beta-sialon was considerably increased to 66% when planetary milled to 18 min after CS. The raw material Si was replaced by waste Si of 94.8 mass% in purity, and was combustion synthesized successfully under the same processing parameters for cost-effective measures.