A catalyst deterioration diagnosis method for diagnosing deterioration of a catalyst for purification of exhaust gas by using a test catalyst disposed in an exhaust gas flow path through which the exhaust gas flows, the method including an exhaust gas control step of inverting an air-fuel ratio of the exhaust gas in the flow path from a lean side to a rich side or from a rich side to a lean side; a measurement step of measuring a change over time in electrical resistance of the test catalyst at the inversion of the air-fuel ratio and finding a resistance change ratio of the test catalyst; and a determination step of determining catalytic deterioration of the test catalyst based on the resistance change ratio.