The nanocrystalline WC-10Co composite powders were produced with the processing method of spray thermal decomposition-continuous reduction & carburization. The grain growth inhibitors of 0.4wt％ Cr3C2 and 0.4wt％ VC were added into the composite powders to obtain advanced ultrafine hardmetals with minimal porosity, defects and discontinuous. The rod samples were formed by extrusion.They were sintered in cacuum with SIP treatment. The sintered rods were made into PCB microdrill samples after polishing. Mechanical properties(such as density, hardness, transverse rupture strenth(TRS), magnetic saturation induction and magnetic coercivity) of the sintered ultrafine cemented carbides were measured. The microstructures of them were investigated by scanning electron microscopy(SEM) and transmission electron microscopy(TEM). The experimental results show that the transverse rupture strength of the samples sintered in vacuum with sinterhip(SIP) treatment is more excellent. The grain size could be controlled in a range of 200-400 nm with the help of grain growth inhibitors. And the superfine grained materials have superior strength(3900 MPa) and high hardness(HRA = 93.3). These features are ideal for PCB microdrills.