An air conditioner for a vehicle, which includes an air conditioning case having an air passage formed therein, a cooling heat exchanger provided in the air passage of the air conditioning case to heat-exchange with air passing through the air passage, and a heating heat exchanger, comprises: a front seat temperature door which adjusts an opening degree between a front seat cold air passage and a part of a hot air passage; a first rear seat temperature door which is disposed between the cooling heat exchanger and the heating heat exchanger and adjusts an opening degree of another part of the hot air passage; and a second rear seat temperature door which is disposed in the downstream of the heating heat exchanger and adjusts an opening degree between the hot air passage and a rear seat cold air passage, wherein the second rear seat temperature door includes an asymmetric dome.