The failure in an adhesive-bonded structure starts at the interface, and the interfacial fracture is of interest whenever adhesion between different materials is concerned. One of primary factors limiting the application of adhesive-bonded joints to structural design is the lack of a good evaluation tool for adhesion strength to predict the load-bearing capacity of boned joints. The adhesion strength of composite/steel bonding has been evaluated using interfacial fracture mechanics characterization. The energy release rate of a composite/steel interfacial crack was compared with the fracture toughness of the interface, which was measured from bi-material end notched flexure (ENF) specimens, to predict the failure loads of bi-material lap joints. Fracture toughness, IIc G , was regarded as a property of the interface rather than a property of the adhesive. The results show that interfacial fracture mechanics characterization of adhesion strength can be a practical engineering tool for predicting the load-bearing capacities of adhesive-bonded joints.