Abstract Interfacial atomic structures of Cu/Al 2O 3(0001) and Cu/Al 2O 3(112̄0) systems prepared by a pulsed-laser deposition technique have been characterized by using high-resolution transmission electron microscopy (HRTEM). It was found that Cu metals were epitaxially oriented to the surface of Al 2O 3 substrates, and the following orientation relationships (ORs) were found to be formed: (111) Cu//(0001)Al 2O 3, [1 1 ̄ 0] Cu//[11̄00]Al 2O 3 in the Cu/Al 2O 3(0001) interface and (001) Cu//(112̄0)Al 2O 3, [11̄0] Cu//Al 2O 3 in the Cu/Al 2O 3(112̄0) interface. Geometrical coherency of the Cu/Al 2O 3 system has been evaluated by the coincidence of reciprocal lattice points method, and the result showed that the most coherent ORs were (111) Cu//(0001)Al 2O 3, [112̄] Cu//[11̄00]Al 2O 3 and (11̄0) Cu//(112̄0)Al 2O 3,  Cu//Al 2O 3, which are equivalent to each other. These ORs were not consistent with the experimentally observed ORs, and it was possible that crucial factors to determine the ORs between Cu and Al 2O 3 were not only geometrical coherency, but also other factors such as chemical bonding states. Therefore, to understand the nature of the interface atomic structures, the electronic structures of the Cu/Al 2O 3 interfaces have been investigated by electron energy-loss spectroscopy. It was found that the pre-edge at the lower energy part of the main peak appeared in the O-K edge spectra at the interface region in both the Cu/Al 2O 3(0001) and Cu/Al 2O 3(112̄0) systems. This indicates the existence of Cu–O interactions at the interface. In fact, HRTEM simulation images based on O-terminated interface models agreed well with the experimental images, indicating that O-terminated interfaces were formed in both systems. Since the overlapped Cu atomic density in the experimental ORs were larger than that in the most coherent OR, it is considered that the on-top Cu–O bonds stabilize the O-terminated Cu/Al 2O 3 interfaces.