Effect of thermal aging on the lap-shear properties of an acrylic-cored laminated steel was investigated by shear testing of specimens following exposure in air to the paint bake temperature of 180 degrees C. The laminated steel consists of two thin steel layers bonded to a polymer core. It was found that thermal aging caused an increase in shear modulus and a decrease in ductility. Shear strength initially decreased, but then increased with aging time. Fractographic, thermal gravimetric, and differential scanning calorimetric analyses indicated that the decrease in shear strength and ductility is likely caused by void formation resulting from evaporation of the volatiles in the acrylic. These voids increased the local stresses. The subsequent increase in shear strength is attributed to the increase in adhesive cross-linking from thermal curing which hardens the adhesive. The increase in shear modulus with increase in aging time is ascribed primarily to thermal curing.