The present invention relates to an air conditioner for vehicle including a front seat air conditioning unit and a rear seat air conditioning unit. The rear seat air conditioning unit has a rear seat air conditioning casing provided with a rear seat evaporator disposed in generally horizontal direction to air flow passages therein, with a rear seat heater core disposed over the rear seat evaporator, with vent outlets and floor outlets disposed on the upper and lower portions of the exit end thereof for discharging the air flowing from the air conditioner to the rear seats of the vehicle, with a rear seat partition wall adapted to divide the air flow passages into two areas, with rear seat temperature doors disposed between the rear seat evaporator and the rear seat heater core, for adjusting the temperatures of the divided areas by the rear seat partition wall, with rear seat mode doors disposed adjacent to the vent outlets and the floor outlets for controlling the degree of opening of the vent outlets and the floor outlets, and with a rear seat blower housed at one side thereof for blowing the air to the rear seat air conditioning casing.