An abnormality diagnosis system for an air-fuel ratio sensor provided in an exhaust passage of an internal combustion engine and generating a limit current corresponding to an air-fuel ratio, comprising: a current detecting part configured to detect an output current of said air-fuel ratio sensor ; and a sensor temperature control device configured to control a temperature of said air-fuel ratio sensor , said system is configured to perform a first control of the output current consisting to control the temperature of said air-fuel ratio sensor to a first temperature (T 1 ) by said sensor temperature control device, and to detect the output current of said air-fuel ratio sensor by said current detecting part , when said internal combustion engine controls the air-fuel ratio so that the air-fuel ratio of the exhaust gas flowing around said air-fuel ratio sensor becomes a rich air-fuel ratio in the state where the temperature of said air-fuel ratio sensor is made the first temperature (T 1 ), said system is configured to perform a second control of the output current consisting to control the temperature of said air-fuel ratio sensor to a second temperature (T 2 ) higher than said first temperature (T 1 ) by said sensor temperature control device, and to detect the output current of said air-fuel ratio sensor by said current detecting part , when said internal combustion engine controls the air-fuel ratio so that the air-fuel ratio of the exhaust gas flowing around said air-fuel ratio sensor becomes a rich air-fuel ratio in the state where the temperature of said air-fuel ratio sensor is made said second temperature (T 2 ), and said system is configured to judge that said air-fuel ratio sensor has become abnormal when the output current when controlling the temperature of said air-fuel ratio sensor to said second temperature (T 2 ) is larger than the output current when controlling the temperature of said air-fuel ratio sensor to said first temperature (T 1 ) by a predetermined value or more. a current detecting part configured to detect an output current of said air-fuel ratio sensor ; and a sensor temperature control device configured to control a temperature of said air-fuel ratio sensor , said system is configured to perform a first control of the output current consisting to control the temperature of said air-fuel ratio sensor to a first temperature (T 1 ) by said sensor temperature control device, and to detect the output current of said air-fuel ratio sensor by said current detecting part , when said internal combustion engine controls the air-fuel ratio so that the air-fuel ratio of the exhaust gas flowing around said air-fuel ratio sensor becomes a rich air-fuel ratio in the state where the temperature of said air-fuel ratio sensor is made the first temperature (T 1 ), said system is configured to perform a second control of the output current consisting to control the temperature of said air-fuel ratio sensor to a second temperature (T 2 ) higher than said first temperature (T 1 ) by said sensor temperature control device, and to detect the output current of said air-fuel ratio sensor by said current detecting part , when said internal combustion engine controls the air-fuel ratio so that the air-fuel ratio of the exhaust gas flowing around said air-fuel ratio sensor becomes a rich air-fuel ratio in the state where the temperature of said air-fuel ratio sensor is made said second temperature (T 2 ), and said system is configured to judge that said air-fuel ratio sensor has become abnormal when the output current when controlling the temperature of said air-fuel ratio sensor to said second temperature (T 2 ) is larger than the output current when controlling the temperature of said air-fuel ratio sensor to said first temperature (T 1 ) by a predetermined value or more. <EOS>