Disclosed are an air conditioner and a refrigerant control method thereof. An air conditioner according to an embodiment of the invention an outdoor unit including a compressor, an outdoor heat exchanger, and a four-way valve that switches a flow passage of refrigerant, an indoor unit including an indoor heat exchanger, an indoor expansion unit disposed at a refrigerant inlet side of the indoor heat exchanger and allowing the refrigerant to be expanded during the cooling operation, an outdoor expansion unit disposed at a refrigerant inlet side of the outdoor heat exchanger and allowing the refrigerant to be expanded during the heating operation, and a control unit controlling the indoor expansion unit and the outdoor expansion unit such that the refrigerant is expanded in the indoor expansion unit during the cooling operation and the refrigerant is expanded in the outdoor expansion unit during the heating operation. Therefore, the distance between the evaporator and the expansion unit is reduced to thereby raise operating efficiency.