A variable displacement vane compressor for an air conditioning system used in an automobile has a cylinder assembly having a bore which receives a rotor to form at least one crescent or compressing chamber between the rotor and the bore. The crescent chamber receives a refrigerant which is returned from the air conditioning system. The rotor has vanes which are extendably fitted therein so that the free end of the vanes are in contact with the circumferential inner surface of the bore during the rotation of the rotor, whereby when the vane passes through the crescent chamber, the refrigerant received therein can be compressed. The amount of the refrigerant introduced into the crescent chamber is adjustable in response to a change of a cooling load at the air conditioning system.