Provided are a foreign substance detecting circuit, an electronic device including the foreign substance detecting circuit, and a method of detecting foreign substance. The electronic device includes a connector connected to an external cable and including a plurality of pins, a foreign substance detecting circuit configured to, when the cable is connected to the connector, detect a resistance from a first pin that is set to be in an open state or to be connected to a pull-down resistor from among the plurality of pins in a state where the cable is connected, and determine whether there is a foreign substance in the connector, and an application processor configured to control operations in the electronic device for performing a post-process when there is the foreign substance in the connector, according to a detection result from the foreign substance detecting circuit.