Silicon nitride/boron nitride nano/nano-composites were prepared by high energy ball milling and spark plasma sintering. The milling promoted the amorphization of starting powders with the presence of many homogeneous distributed nanocrystalline â-Si3N4 particles; most of the BN particles were transformed into nano-size and embedded in the amorphous phase. This, combined with low sintering temperature and rapid densification rate, leads to a uniform nano/nano composite microstructure. The nano-sized BN grains with an average diameter of about 10 nm were homogeneously dispersed in nano-sized (about 70 nm) Si3N4 grain boundaries. The obtained nano/nano composite shows high hardness, high strength, high superplasticity, good heat/corrosion resistance and good tribological properties.