Provided is a vehicle air-conditioning system configured so that air-cooling/heating can be efficiently performed. The system (10, 20, 30, 40) includes a vapor compression heat pump unit (HP) having at least a compressor (CP), a condenser (CD), an expansion mechanism (EX), and an evaporator (EV) on a refrigerant circuit (RC), a brine flow path network (BC) having multiple pumps (PC, PH) and multiple flow path switching valves (TV1 to TV8, V1 to V9), and a vehicle indoor air-conditioning unit (AC) having an air duct (AD) and multiple vehicle indoor heat exchangers (HXC1, HXC2) arranged in series in the air duct. Upon actuation in an air-cooling mode or an air-heating mode accompanied by neither dehumidification nor defrosting, brine flows in series in the multiple vehicle indoor heat exchangers.