Composites consisting of 70vol% ZrB2 and 30vol% alpha-SiC particles were hot pressed to near full density and subsequently annealed at temperatures ranging from 1000 degrees C to 2000 degrees C. Strength, elastic modulus, and hardness were measured for as-processed and annealed composites. Raman spectroscopy was employed to measure the thermal residual stresses within the silicon carbide (SiC) phase of the composites. Elastic modulus and hardness were unaffected by annealing conditions. Strength was not affected by annealing at 1400 degrees C or above; however, strength increased for samples annealed below 1400 degrees C. Annealing under uniaxial pressure was found to be more effective than annealing without applied pressure. The average strength of materials annealed at 1400 degrees C or above was similar to 700MPa, whereas that of materials annealed at 1000 degrees C, under a 100MPa applied pressure, averaged similar to 910MPa. Raman stress measurements revealed that the distribution of stresses in the composites was altered for samples annealed below 1400 degrees C resulting in increased strength.