A chemical process for fabrication of Si3N4/BN nanocomposite was devised to improve the mechanical properties. Si3N4/BN nanocomposites containing 0 to 30 vol% hexagonal BN (h-BN) were successfully fabricated by hot-pressing alpha-Si3N4 powders, on which turbostratic BN (t-BN) with a disordered layer structure was partly coated. The t-BN coating on alpha-Si3N4 particles was prepared by reducing and heating alpha-Si3N4 particles covered with a mixture of boric acid and urea. TEM observations of this nanocomposite revealed that the nanosized hexagonal BN (h-BN) particles were homogeneously dispersed within Si3N4 grains as well as at grain boundaries. As expected from the rules of composites, Young's modulus of both micro-and nanocomposites decreased with an increase in h-BN content, while the fracture strength of the nanocomposites prepared in this work was significantly improved, compared with the conventional microcomposites.