A state determining apparatus for an exhaust gas recirculation system is provided for appropriately determining the state of an exhaust gas recirculation system including an EGR passage. An exhaust gas recirculation system is arranged in an exhaust system of an internal combustion engine including an EGR passage for recirculating a portion of exhaust gases to an intake system in accordance with an operating state of the internal combustion engine. The state determining apparatus comprises a humidity sensor arranged in the EGR passage for detecting a humidity within the EGR passage, and an ECU for determining the state of the exhaust gas recirculation system based on a result detected by the humidity sensor.