Reaction zone phases and kinetics over a temperature range of 650-1200°C have been characterized for Ti-14Al-21Nb/SiC and Ti-6Al-2Sn-4Zr-2Mo/SiC fibrous composites. The matrix of the Ti-1421/SiC materials was α2 with varying amounts of beta phase and transformed beta phase, and the Ti-6242 matrix consisted of alpha plus beta. The reaction zone in the as-HIP Ti-1421/SiC contained fine-grained TiC, a region of coarser-grained TiC, a carbide layer containing Ti, Al and Nb, and a region of(Ti, Nb)5(Si, Al)3. The matrix adjacent to the reaction zone was α2-Ti3Al with no beta phase. In the as-HIP Ti-6242/SiC composites, the reaction zone contained TiC near the fiber, and a layer of (Ti,Zr)5Si3 adjacent to the matrix. In heat-treated samples, the reaction zone thicknesses varied in a linear fashion with the square-root of aging time, indicating diffusion-controlled growth. Incubation periods for reaction zone growth were observed in Ti-1421/SiC samples aged at 760-1000°C. The overall kinetics for the two matrix alloys were approximately the same, and the activation energy was measured as 63-73 kcal/mole for Ti-1421/SiC and 73kcal/mole for Ti-6242/SiC.