Abstract This work reported submicrometric HfB 2 powder synthesis by a new borothermal reduction route using HfO 2 and boron as raw materials. The particle size of HfB 2 powders by conventional borothermal reduction was ~ 2.1 μm. HfB 2 particle coarsening mainly depended on the presence of B 2 O 3 product. To obtain HfB 2 powders with small particle size, new borothermal reduction route was developed. This route included the borothermal reduction of HfO 2 with boron at 1100 °C, washing by hot water, and the removal of residual B 2 O 3 at 1550 °C, namely, two-step reduction plus intermediate water-washing. Based on the new route, the particle size of HfB 2 powders decreased to ~ 0.8 μm. Finally, the hot-pressing densification of the synthesized powders was studied.