Fine amorphous silicon nitride powders were prepared by vapor phase reaction between nitrogen-containing, chloride-free organosilicon compound and NH3 at the production rate of-200g/h. Crystallization was carried out by heat treating the resulting amorphous powders in Ar atmosphere at 1500°C. High purity crystalline silicon nitride powders could be synthesized with metallic impurities Fe, Al, Ca<50ppm, carbon content <1wt% and oxygen content of -1wt%. The specific surface area, mean particle size and a phase content were-10m2/g, 0.6μm and >95wt%, respectively. Mechanical properties of hot-pressed silicon nitride from the resulting crystalline powders were comparable to hot-pressed bodies fabricated from high purity silicon nitride powders by imide decomposition and carbothermic reduction of silica.