A silencer for a vehicle air conditioning system is designed to reduce a noise and a vibration of a compressor transmitted into a vehicle room along coolant pipes. The silencer includes a silencer body tube and an external resonance tube. The silencer body tube is installed between the coolant pipes wherein a coolant gas flowing along the coolant pipes passes through the silencer body tube, the silencer body tube including one or more resonance holes formed on an outer circumferential surface of the silencer body tube. The external resonance tube is installed on the outer circumferential surface of the silencer body tube wherein a resonance chamber for absorbing a vibration and a noise of a coolant gas flowing through the silencer body tube is defined between the outer circumferential surface of the silencer body tube and the external resonance tube.