An abnormality diagnosis system for an air-fuel ratio sensor (40, 41) provided in an exhaust passage (19, 21) 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 (40, 41); and a sensor temperature control device configured to control a temperature of said air-fuel ratio sensor (40, 41), said system is configured to perform a first control of the output current consisting to control the temperature of said air-fuel ratio sensor (40, 41) to a first temperature (T 1) by said sensor temperature control device, and to detect the output current of said air-fuel ratio sensor (40, 41) 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 (40, 41) becomes a rich air-fuel ratio in the state where the temperature of said air-fuel ratio sensor (40, 41) 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 (40, 41) 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 (40, 41) 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 (40, 41) becomes a rich air-fuel ratio in the state where the temperature of said air-fuel ratio sensor (40, 41) is made said second temperature (T 2), and said system is configured to judge that said air-fuel ratio sensor (40, 41) has become abnormal when the output current when controlling the temperature of said air-fuel ratio sensor (40, 41) to said second temperature (T 2) is larger than the output current when controlling the temperature of said air-fuel ratio sensor (40, 41) 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 (40, 41); and a sensor temperature control device configured to control a temperature of said air-fuel ratio sensor (40, 41), said system is configured to perform a first control of the output current consisting to control the temperature of said air-fuel ratio sensor (40, 41) to a first temperature (T 1) by said sensor temperature control device, and to detect the output current of said air-fuel ratio sensor (40, 41) 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 (40, 41) becomes a rich air-fuel ratio in the state where the temperature of said air-fuel ratio sensor (40, 41) 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 (40, 41) 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 (40, 41) 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 (40, 41) becomes a rich air-fuel ratio in the state where the temperature of said air-fuel ratio sensor (40, 41) is made said second temperature (T 2), and said system is configured to judge that said air-fuel ratio sensor (40, 41) has become abnormal when the output current when controlling the temperature of said air-fuel ratio sensor (40, 41) to said second temperature (T 2) is larger than the output current when controlling the temperature of said air-fuel ratio sensor (40, 41) to said first temperature (T 1) by a predetermined value or more.