The fracture strength of GFRP/stainless-steel adhesive joints reinforced with glass mat was studied analytically and experimentally. First, the stress distributions near the bonding edge were analyzed with FEM. The FEM results showed that the shear stress and the normal stress distributions near the bonding edge can be expressed by two stress singularity parameters. Second, to measure the delamination initiation load, tensile shear tests were conducted on taper lap joints and those reinforced with glass mat. The experimental results showed that the delamination strength of taper lap joints reinforced with glass mat can be evaluated with stress singularity parameters, and reinforcing the bonding edge with glass mat effectively enhanced adhesive joint strength.