In this article, the microstructure, mechanical properties and machinability of the B4C/BN microcomposites and the B4C/BN nanocomposites were investigated. Homogenous distribution of the h-BN particles in the B4C ceramics appeared. The mechanical properties decreased gradually with the increasing content of h-BN for the both composites, while the nanocomposites demonstrated high performance. Machinability increased gradually with the increasing content of h-BN, and excellent machinability exhibited for both composites with more than 20wt% h-BN. The weak interface between the B4C matrix grains and the h-BN particles as well as the cleavage behavior of the laminate structured h-BN particles significantly attributed to the machinability of the B4C/BN composites.