With adding various contents of combined grain growth inhibitors (GGI) VC and Cr3C2 into the ultrafine WC-Co composite powder, the effects of the GGI addition on the phase constitution, microstructure and mechanical properties of the cemented carbides have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The result shows that with the content of GGI increasing in the composite powder, the abnormal grain growth disappears and homogeneous ultrafine grain structure forms. The hardness of cemented carbides can be improved effectively with increasing the addition of VC, while enhancements of the transverse rupture strength (TRS) depends more on the Cr3C2 addition.