Nano-sized WC particles in WC/Co composite powders were synthesized by mechanochemical method. The raw powders(WO3, Co3O4, VC, Cr3C2 and graphite) were mixed by planetary milling with ethyl alcohol for 30 hours. The compositions were WC-10 and -20 wt% Co after reduction and carburization. The powders of VC and Cr3C2 were added as the inhibitors to inhibit the formation of nano-sized WC particles. The direct reduction and carburization of the oxides with carbon were carried at 900°C for 1 to 3 hours under flowing Ar gas. The resultant powders were compacted and sintered at 1300~1360°C for 0.5 hour. The degree of the direct reduction and carburization of the mixed powders increased with the reaction time. The mean size of WC particles in WC/Co composite powders was about 16 nm, and the mean size of WC/Co composite powders was about 240 nm. In WC-10 and -20 wt% Co, the sintered compacts shrank by 16% and 24%, respectively. The mean sizes of WC in WC/Co composite powders were about 50 and 30 nm.