The interfacial fracture energy of Ti/Al2O3 composites was measured with and without a diffusion barrier at different bonding temperatures by using four-point bending tests. It was found that the interfacial fracture energy increases with increasing bonding temperature up to 950 °C. When the bonding temperature was further raised to 1000 °C, the interfacial fracture energy drops. The decrease of the interfacial fracture energy is due to the formation of the continuous intermetallic compound, Ti3Al, at the interface between Ti and A12O3. By using a diffusion barrier, the interfacial fracture energy decreases from 25.4 to near 0 J/m2 and 32.9 to 8.7 J/m2 for applied bonding temperatures of 800 and 900 °C, respectively. This is because the diffusion barrier reduced the diffusion of A1 across the interface and into the Ti, thereby preventing a strong chemical bond at the interface. For the composite bonded at 900 °C, the crack propagation was found to occur at the interface between the Ti and A12O3. The interfacial failure was found to be in the Ti3Al reaction layer for the composite processed at 1000 °C. With a diffusion barrier, the crack propagation path follows several interfaces. Evaluation of the processing temperature on the mechanical properties of the Ti was also obtained by using a nanoindentation technique.