A vehicular air conditioning system includes: a refrigerant circulation line including first and second evaporators through which refrigerant can flow in a cooling mode, and first and second expansion valves configured to depressurize and expand the refrigerant introduced into each of the first and second evaporators; and refrigerant flow control part provided in front of the first evaporator and the first expansion valve and configured to control refrigerant flow. The first evaporator is used for cooling rear seat region of a passenger room and the refrigerant flow control part is configured to supply and block the refrigerant with respect to the first evaporator and the first expansion valve and is configured to block the refrigerant when the cooling governed by the first evaporator is controlled in a turn-off mode and supply the refrigerant to the first evaporator and the first expansion valve depending on the on/off condition of the cooling governed by the second evaporator.