An air conditioner for a vehicle includes: a casing to accommodate a cooler and a heater; a front temp door disposed in the casing to control a temperature of air supplied to a front seat zone; a rear temp door disposed under the front temp door to control a temperature of air supplied to a rear seat zone; and a rear vent disposed at a lower portion of the casing to discharge air to the rear seat zone. The air conditioner can secure the flow rate of the air that is supplied to the rear seat zone of the interior of a vehicle by improving the route for flow of the air that is supplied to the rear seat zone.