The ultrafine WC-0.5Co cemented carbide with a grain size smaller than 0.5 μm was prepared by high energy ball milling and HIP-sintering process. The raw materials were ultrafine WC and WC-0.5Co powder and the additives of grain growth inhibitor were VC/Cr3C2 and carbon. Microstructure and properties of the ultrafine WC-0.5Co cemented carbide with different VC/Cr3C2 and carbon contents were studied. The results show that there is a significant effect of VC/Cr3C2 on controlling WC particle size and hardness of ultrafine WC-0.5Co cemented carbide. Ultrafine WC-0.5Co cemented carbide has best Vickers hardness HV0.05 of 32 658 MPa with the VC/Cr3C2 content of 0.73% (mass fraction, similarly hereinafter). A certain amount of mixed carbon content is good for decarburization and properties of the ultrafine binderless cemented carbide. Ultrafine WC-0.5Co-073VC/Cr3C2 cemented carbide has best comprehensive mechanical properties with transverse rupture strength of 6.935 MPa·m1/2 and Vickers hardness HV0.05 of 32 216 MPa when the mixed content of carbon is 0.2%