A proximity sensor and a mobile communication device thereof are provided. The mobile communication device includes an antenna structure, a matching circuit, a capacitance sensing circuit and a processing circuit. The matching circuit couples to the antenna structure. The capacitance sensing circuit couples to the matching circuit. The capacitance sensing circuit senses a capacitance variation on the antenna structure via the matching circuit and accordingly generates a proximity sensing signal. The processing circuit is coupled to the capacitance sensing circuit to receive the proximity sensing signal. When a signal level of the proximity sensing signal exceeds a first threshold value, an object is determined approaching, and when the signal level of the proximity sensing signal exceeds a second threshold value, a human body is determines approaching. The first and the second threshold value are different.