The effect of WC particle size with the addition of VC as a grain growth inhibitor was investigated during the liquid phase sintering of WC-Co system. With increasing WC particle size at the same VC content, the effect of grain growth inhibition was increased. Also, with increasing the VC content, the grain shape of WC was changed from the faceted shape to the distorted shape, and the step density of the WC grain was increased. WC-Co system is widely used as machining tools for practical purposes due to their excellent hardness, strength, and wear-resistance. The mechanical properties of WC-Co systems are known to be strongly dependent on the grain size of WC; the smaller grain size of carbide show the higher mechanical properties [1]. So far, the addition of grain growth inhibitors such as VC, TiC, Cr2C3, and NbC has been recognized to be an effective method to obtain the small grain size of WC [2-5]. Such carbide addition is believed to play an important role for the inhibition of grain growth during liquid phase sintering. However, the detailed mechanism of grain growth inhibition has not been clarified yet. Recently, some researchers reported that the grain growth inhibition could be corelated with the shape change of WC grain due to the addition of inhibitors [6]. In this study, the effect of WC particle size on grain growth inhibition and grain growth behavior in WC-Co systems was investigated with the addition of VC. In order to suppress any additional change of microstructure during cooling, some specimens were water-quenched to suppress any additional change of microstructure during cooling. The shape change of WC grain was observed using SEM and TEM. In order to observe the 3-dimensional grain shape of WC, sintered specimen was Zn-alloyed, and then the matrix was removed using dilute hydrochloric acid.