A simple thermal decomposition technique to convert asbestos-containing wastes (ACWs) into non-asbestos products has been developed by heating ACWs in a water vapor atmosphere. It was confirmed that cement slates containing 18 mass % chrysotile were converted into non-asbestos products by the thermal treatment in a water vapor atmosphere at 800°C for 2 h. In contrast, the thermal treatments in air required temperatures as high as 900°C to convert the cement slates into non-asbestos products. It should be noted that any chrysotile particles were not detected by the phase-contrast microscopic observation in the products after the thermal treatments in a water vapor atmosphere at temperatures beyond 800°C but three or less chrysotile particles remained after the thermal treatments in air at high temperatures beyond 900°C. In a water vapor atmosphere, ACWs were successfully converted into non-asbestos products at low temperatures below 800°C for 2 h by accelerated solid-state reactions between decomposed products of chrysotile and cement components to form calcium magnesium silicates. This technique may contribute to large-scale decomposition of ACWs with low energy consumption in comparison with the traditional melting method.