The effects of the addition of cobalt metal on the densification and the mechanical properties of TiB₂-Co alloys under the pressureless-sintering as well as the hot-pressing conditions were examined. A dense TiB2-based alloy could be obtained by the addition of Co by either the pressureless-sintering or the hot-pressing process. The TiB₂-2vol% and 6vol%Co alloys hot-pressed at the temperature from 1600 to 1800°C for 1 hr in vacumm under 6OMPa had the bending strength of 940MPa. The TiB2-l0vol%Co alloy pressure-less sintered at the temperature of 1800°C for 1 hr in vacuum had the bending strength of 64OMPa. The hot-pressed alloys with Co had a finer grain size compared with the pressureless-sintered alloys. The hardness of the pressur-less sintered TiB₂-Co alloys were higher than that of TiB₂. In the TiB₂-Co system, Co metal changes completely to borides.