Concrete is a kind of multiphase material, which consists of three phases, including cement paste, aggregate and the interfacial transition zone (ITZ) between cement paste and aggregate. In the three phases, the interfacial transition zone is the weakest phase, especially the interfacial transition zone between cement paste and coarse aggregate. In this paper, the influence of aggregate size and type on the bonding strength at the ITZ was experimentally investigated. Splitting tensile test and compression shear test were used to obtain the bonding strength and shear strength between aggregate and cement paste. It is found that aggregate size has a great effect on the bonding strength at the ITZ. The bonding strength at ITZ decreases with increasing aggregate size. When the water/cement ratio is lower, it could get higher bonding strength at the ITZ. And also, the aggregate type has a great effect on the bonding strength at the ITZ.