We performed in‐situ XAS study of N2O decomposition over CuO/CeO2 catalysts. The Cu K‐edge and Ce L3‐edge XANES and EXAFS analyses revealed the dynamic and crucial role of Cu2+/Cu+ and Ce4+/Ce3+ ionic pairs during the catalytic reaction. We observed the initial formation of reduced Cu+ and Ce3+ species during activation in helium atmosphere at 400 °C, while concentration of these species decreased significantly during steady‐state nitrous oxide degradation reaction (2500 ppm N2O in He at 400 °C). In‐situ EXAFS analysis further revealed a crucial role of copper−ceria interface in this catalytic reaction. We observed dynamic changes in average number of Cu−Ce scatters under reaction conditions, indicating an enlarging of the interface between both copper and ceria phases, where electron and oxygen transfer occurs. Mechanistic study: In‐situ XAS study of N2O decomposition over CuO/CeO2 catalysts revealed the crucial role of copper−ceria interface and participating of Cu2+/Cu+ and Ce4+/Ce3+ ionic pairs in the catalytic cycle.