A continuous two-stage carburization furnace whose first furnace has a nitrogen atmosphere and whose second one has a hydrogen atmosphere was developed. A mixture of WO₃ and C was pelletized and resulting powders were heated continuously as they moved from the first furnace to the second furnace. The severe control of the carbon content of the product was possible by this two-step carburization method. The grain size of WC powder could easily be controlled by the heating temperatures of the first and the second furnaces. The grain size distribution thus obtained was uniform and narrow.