Experiments were conducted by hot-pressing to densify HfB2 commercial powders using HfSi2 (5 vol%) or B4C (7 vol%) as sinter additives. The former was very effective as sintering enhancer: 15 min at 1,600 degrees C was a sufficient condition to achieve near full density. The occurrence of a liquid phase sintering, which substantially enhanced densification during hot- pressing, was found out. The HfB2-B4C powder mixture, hot-pressed at 1,900 degrees C for 40 min, achieved a relative density of 94%. Aside the key role of sintering enhancer, B4C also allowed the development of a uniform microstructure, preventing an excessive growth of the diboride matrix (2 mu m mean size). On the contrary, thanks to the liquid phase that sustained substantial transfer of mass during heating, the HfSi2-doped composition had an uneven and more obvious grain growth (4 mu m mean size), with faceted diboride grains up to 10 mu m.