Ultra fine tungsten carbide and cobalt powders were milled by high energy planetary ball mill at different ball to powder weight ratios (BPR) to produce particles of WC–10 wt%Co hard metal in nanometer scale size. Microstructural characterizations by TEM show that the particle size of tungsten carbide was achieved to 32 nm after milling at 15 BPR during 10 h. In order to reduce the WC grain growth during the sintering process, tantalum carbide was added to the hard metal as a WC grain growth inhibitor. The nano hard metal powders were compacted at 200 MPa pressure and sintered at 1370–1450 °C temperatures in a high purity hydrogen atmosphere. The results show that the addition of 0.6 wt% of TaC improves the hardness and fracture toughness from 1493 HV₃₀ and 11.8 MPa√m (for TaC free sample) to 1614 HV₃₀ and 13.7 MPa√m, respectively.