Abstract: With the ultrafine W powder (0.35 μm) and carbon black powders of various shes(0.1, 0.3, 0.8, 4.5 μm), the influences of carbon black pride size and carburization temperatures(830-1300℃ for 40 min) on the compounded carbon content and phase compositions in WC powders were investigated at the atmosphere of H2. The adding amount of carbon was determined under the reaction equation of W+C=WC. The phase compositions of the reacted products were analyzed by XRD. The experimental results demonstrated that when ultrafine carbon of 0. 1 μm was used, the compounded carbon content in the WC powders was up to 5.8%(mass fraction), corresponding to 95% of the theoretical content, at very low temperature of 850℃; when the temperature was higher than 930℃, the carbon content of WC powders approached the theoretical one. It is concluded that carburization can be completed at very low temperature when the ultrafine carbon black powders are used, in which the ultrafine W particles are carbonized before the they begin to grow and form W aggregation.