Disclosed are an air conditioner in which one or more compressors are operated so that the refrigerant compression capacity of the operating compressor(s) is variably changed in accordance with a cooling or heating load for cooling or heating air in a room, and a method for controlling an electronic expansion valve of the air conditioner. The air conditioner comprises a plurality of compressors for compressing a refrigerant; a condenser for condensing the refrigerant; an electronic expansion valve for expanding the refrigerant; an evaporator for evaporating the refrigerant; a direction change valve for changing the flow direction of the refrigerant; a refrigerant pipe for connecting the compressors, the condenser, the electronic expansion valve, the evaporator and the direction change valve; and a microcomputer for controlling the operation of the air conditioner, wherein an opening degree of the electronic expansion valve is controlled so that a current degree of superheat coincides with a target degree of superheat set in consideration of the refrigerant compression capacity of operating compressor(s) and an outdoor temperature. The air conditioner prevents the refrigerant in a liquid state from being introduced into the compressor(s) and the compressor(s) from overheating, and rapidly eliminates the cooling or heating load.