The construction of stable active site in nanocatalysts is of great importance but is a challenge in heterogeneous catalysis. Unexpectedly, coordination-unsaturated and atomically dispersed copper species were constructed and stabilized in a sintered copper-ceria catalyst through air-calcination at 800 degrees C. This sintered copper-ceria catalyst showed a very high activity for CO oxidation with a CO consumption rate of 6100 mu mol(CO).g(Cu)(-1).s(-1) at 120 degrees C, which was at least 20 times that of other reported copper catalysts. Additionally, the excellent long-term stability was unbroken under the harsh cycled reaction conditions. Based on a comprehensive structural characterization and mechanistic study, the copper atoms with unsaturated coordination in the form of Cu1O3 were identified to be the sole active site, at which both CO and O-2 molecules were activated, thus inducing remarkable CO oxidation activity with a very low copper loading (1 wt %).