$HfB_2$-HfC composites were prepared by reactive hot pressing using Hf and $B_4C$ at temperatures of 1800 and $1900^{circ}C$ for 60 min under 32 MPa in an Ar atmosphere. The reaction sequences of the $HfB_2$-HfC composite were studied through series of pressureless heat treatments ranging from 800 to $1600^{circ}C$. The effect of size reduction of the starting powders on densification was investigated by vibration milling. Fully dense $HfB_2$-HfC composites were obtained by size reduction of the starting powders via vibration milling. The oxidation behaviour of the $HfB_2$-HfC composites at $1500^{circ}C$ in air showed formation of a non-protective $HfO_2$ scale with linear mass gain. Examination of the mechanical properties showed that particle size reduction via vibration milling also led to improved flexural strength, hardness and fracture toughness.