A method and an apparatus for operating a proximity sensing function of an electronic device including a touch screen are provided. The electronic device detects a request for activating the proximity sensing function, and measures an illuminance value of light received by an illuminance sensor in response to the detected request. If the measured illuminance value is different from a predefined illuminance value, the device changes a threshold of the proximity sensing function, based on the measured illuminance value. The threshold is defined to determine whether an object is approaching the electronic device.