The effects of stearic acid as a process control agent (PCA) on the synthesis of WC-MgO by mechanical alloying have been investigated. 0-2.0 wt% of stearic acid is added into the mixture of WO3, Mg, and graphite powders in high-energy planetary ball milling experiments, and the as-milled powders are characterized by XRD and TEM. Results show that the mechanochemical reaction among WO3, Mg, and graphite to form WC-MgO can be changed from a mechanically induced self-propagating reaction (MSR) to a gradual reaction by the addition of stearic acid in the range from 1.2 to 1.8 wt%, when other milling parameters are maintained at the same level. It has also been found that with the addition of stearic acid, the crystallite and particle size of WC-MgO powders can be refined, the homogeneity of particle size can be improved and the powder yield can be increased.