An experimental method is proposed for obtaining the fracture toughness of an interfacial crack in sandwich structures. The method relates the interfacial fracture toughness with temperature change developed at the crack front. The focus of the paper is the development of an experimental approach that uses high speed infrared (IR) thermography to capture the temperature evolution during the crack growth. The feasibility of using IR thermography is demonstrated on sandwich structure specimens with E-glass/epoxy face sheets and cross-linked PVC H100 foam core loaded in mixed-mode bending. Different crack propagation paths, in the foam core and at the face sheet/core interface are considered. It is shown that IR thermography with 15 kHz frame rate is able to make a quantitative measurement of the crack front temperature associated with the crack growth. A constant of proportionality ? is derived between the temperature change per unit area at the crack front and the fracture toughness provided by a validated FE model. It is shown that ? obtained from specimens with the same crack propagation path is identical, even though the specimen dimensions and loading mode-mixities are different. Thus, it is demonstrated that for a particular interface, once ? is obtained from a known loading condition, the interfacial fracture toughness from any loading configuration can be determined from a direct temperature measurement.