The present invention relates to a method of producing nanophase powder, which can be used as materials for high-strength and wear-resistance cemented carbide. It purports to provide a method of producing WC powder of a 10.about.20 nm grade by using vapor phase reaction with a precursor containing tungsten. For achieving said objectives, the method of producing WC-based powder according to the present invention comprises preparing a precursor containing tungsten; producing gas by vaporizing said precursor in a reactor; and carburizing said gas in a non-oxidizing atmosphere. The nanophase WC powder produced as such has high-strength and excellent wear-resistance, which can be suitably used as materials for carbide tools, carbide cement, wear-resistance components, or metal molds.