Silicon nitride-silicon carbide (Si3N4-SiC) nanocomposites were fabricated by a process involving reaction bonding followed by superplastic sinter-forging. The nanocomposites exhibited an anisotropic microstructure, in which rod-shaped, micrometer-sized Si3N4 grains tended to align with their long axes along the material-flow direction. SIC particles, typically measuring several hundred nanometers, were located at the Si3N4 grain boundaries, and nanosized particles mere dispersed inside the Si3N4 grains. A high bending strength of 1246 +/- 119 MPa, as well as a high fracture toughness of 8.2 +/- 0.9 MPa.m(1/2), was achieved when a stress was applied along the grain-alignment direction.