Disclosed therein is a dual zone type air conditioner for a vehicle, which includes: an air volume control door mounted between a blower and an evaporator for controlling the degree of opening of first and second passageways so as to control the volume of air blown to the inside of an air-conditioning case; and bypass passageways disposed in the air volume control door to supply a predetermined air volume to a closed passageway even though the air volume control door is at the location to close the first passageway or the second passageway, thereby preventing a sudden change in air volume by widening a control interval of the air volume control door because the first-stage air volume can be realized even though the air volume control door closes one of the air passageways, and reducing a whistle noise by securing a predetermined cross-sectional area of the air passageway through the bypass passageways even though the cross-sectional area of the air passageway gets narrower while the air volume control door closes one of the air passageways.