A fine white α-Si3N4 powder has been produced by the thermal decomposition of the coprecipitation product of the reaction between SiC14 and NH3. The Cl content, due to a reaction between Si(NH)2 and the NH4Cl by-product during the thermal treatment of the coprecipitate, has been reduced by using an isothermal step at ≈ 250°C in the heat treatment cycle.