Abstract: A sintered silicon nitride-silicon carbide composite material is provided comprising a matrix phase of silicon nitride and silicon carbide where silicon carbide grains having an average diameter of not more than 1 .mu.m are present at grain boundaries of silicon nitride grains and silicon carbide grains having a diameter of several nanometers to several hundred nanometers, typically not more than about 0.5 micrometers, are dispersed within the silicon nitride grains and a dispersion phase where (a) silicon carbide grains having an average diameter of 2 to 50 .mu.m and/or (b) silicon carbide whiskers having a short axis of 0.05 to 10 .mu.m and an aspect ratio of 5 to 300 are dispersed in the matrix phase. A process for the production of the composite material is also provided.