W nanoparticles derived from WO 3 during heating in H 2 were carburized at 900–1100K in pure, Ar and H 2 -diluted CH 4 atmospheres. It was aimed to elucidate carburization behavior of pre-reduced W powders under various atmospheres and to establish optimal conditions for the synthesis of nanocrystalline WC. Weight measurements, XRD and SEM were used to characterize the products at various stages of the reaction. At 900K, carburization was limited to the formation of W 2 C owing to slow C diffusion. At 1000K, WC particles were obtained within ~75min using the diluted gas mixtures, while under pure CH 4 atmosphere carburization reaction practically stopped due to pyrolytic carbon skin formed on particle surfaces where C supply was more than consumed. WC powders with particle size 40–65nm and grain size 15–25nm were synthesized at 1100K in a short time under the gas atmospheres studied.