Measurement of mixed mode interfacial fracture toughness in Ti/Al2O3 bimaterial couples has been accomplished by four-point bending tests of sandwich specimens with symmetrical cracks for different processing temperatures and thicknesses of Ti interlayers. Fracture surfaces and sample cross sections were analyzed by SEM, XPS, EDAX, EPMA and AES. The interfacial fracture toughness measured with four-point bending tests increases with increasing applied bonding temperature up to 950°C. Above this temperature toughness decreases. The deterioration of toughness is found to be due to an intermetallic phase (Ti3Al) produced by diffusion at high temperature. The interfacial fracture toughness also increases when the Ti interlayer is thicker. The measured critical strain energy release rate (or interfacial fracture energy) ranges from 10 to 45 J/m2. This is much larger than the estimated true work of adhesion which is about 2 J/m2. This is because of plastic energy dissipation in the Ti interlayer during the fracture process.