Recently, bonding patch plate is used for rehabilitation of steel structures deteriorated with corrosion or fatigue cracks. The patch plate tends to decreases the stress intensity factor at crack tip and delay the crack propagation. However, debonding of patch plates could occur around the end of patch plates and at fatigue crack edges. To evaluate debonding of patch plates bonded to the cracked steel plate, axial loading tests for butted steel joint with bonded patch plates were conducted. Furthermore, the shear and normal stresses in adhesive layer were analyzed. The debonding strength of the joint was evaluated from a view of principal stress in adhesive layer.