Display omitted •Cu/CeO2 contains three CuO species, isolated Cu2+, CuO film, and CuO particle.•CuO film shows the highest NO–CO reaction activity than the other species.•Reduction of Cu–O–Ce interface is highly important for Cu/CeO2 catalytic activity. The stoichiometric NO–CO reaction was studied over Cu/CeO2 catalysts prepared with different Cu loadings and specific surface areas of CeO2 to investigate the relationship between catalytic activity and the copper–ceria interaction. XRD, ESR and H2-TPR results revealed that CuO species interacted with CeO2 in three structurally different forms: isolated Cu2+, a highly dispersed CuO film, and large CuO particles. The CuO film showed a higher NO–CO reaction activity than the other species. An Operando XAFS study revealed that the reduction of the CuO film during the NO–CO reaction occurred at the Cu–O–Ce interface. Thus, we concluded that the most suitable CuO structure to effectively exploit Cu–O–Ce interface sites in the NO–CO reaction is a two-dimensionally dispersed CuO film.