Mode-II interlaminar mechanical properties of CFRP/Al(aluminum) laminates were improved by acid treatment to an Al plate and adding vapor-grown carbon fiber (VGCF) between the Al plate and a CFRP layer. The influence of VGCF addition on the Mode-II interlaminar mechanical properties was explored by end-notched flexure tests. The experimental results demonstrated that the critical load and Mode-II fracture toughness of the specimen with acid treatment and 10 g/m(2) addition of VGCF increase by 73.66 and 175.76 %, respectively, compared to those of the specimen with acid treatment only. The improvement mechanisms were investigated by the observation of crack propagation path and fracture surface under laser scanning and scanning electron microscopies. Moreover, finite element analyses were undertaken based on the cohesive zone model to verify the experimental fracture toughness and to predict the interfacial shear strength between the Al plate and the CFRP layer.