Residual stresses were determined in particle-reinforced ceramic composites using synchrotron based x-ray diffraction. The baseline Si3N4 and the Si3N4-TiN composites were processed by turbomilling, pressure casting, and isopressing. They were then continuously sintered to full density, under a pressureless, flowing nitrogen atmosphere. The flexural strength, fracture toughness, and residual stress were measured for as-machined samples and following quenching in water from 1000degreesC, 1100degreesC, and 1200degreesC. The residual stresses for both the baseline Si3N4 and the Si3N4-TiN composites were determined from the (441) and (531) reflections, by applying the 2theta-sin(2)psi method. The measured residual stresses were compared with the flexural strength and fracture toughness results to determine the effects of residual stress and thermal shocking on the mechanical properties of each material. In both the baseline Si3N4 and Si3N4-TiN composites, after thermal shocking, the compressive residual stresses were developed in directions both parallel and perpendicular to the sample surface. The residual compressive stresses for the Si3N4-TiN composites were much higher than the baseline Si3N4. As a result, both fracture toughness and flexural strength of the Si3N4-TiN composites were improved. In addition, the addition of the TiN appears to improve both the strength and toughness of the baseline Si3N4.