Effects of the chemical composition and sintering atmosphere on the formation of reaction phases and physical properties of reactive hot-pressed TiB2-AlN-BN composites were investigated. At N2 atmosphere, TiN was formed by the reaction between Ti and N2, which inhibited the densification and results in inferior mechanical-and electrical properties of the composites. However, at Ar atmosphere, enhanced densification and physical properties of composites were obtained due to that the TiN formation reaction was excluded. Densification of the composites was also hindered by BN, therefore, inferior mechanical-and electrical properties of composites were obtained with amount of BN in the starting materials. At Ar atmosphere, TiB2-AlN-BN composites having 318 MPa of flexural strength, 3.5 MPa.m1/2 of fracture toughness and 276$mu$Ω.cm of electrical resistivity were fabricated from mole ratio 1:2:1.6 of Ti-Al-BN mixtures.