A heat pump system for a vehicle may include an outdoor condenser, an expansion valve, an evaporator, a compressor, and an indoor condenser that primarily condenses the refrigerant compressed through the compressor and is connected with the outdoor condenser, in which the outdoor condenser, the expansion valve, the evaporator, the compressor, and the indoor condenser are connected through refrigerant pipes, a first valve disposed in the refrigerant pipe between the outdoor condenser and the expansion valve; a chiller connected with the first valve through the refrigerant pipe, between the evaporator and the compressor, and controls the temperature of the refrigerant by exchanging heat; a connection pipe selectively allowing some of the refrigerant flowing into the chiller in a dehumidifying mode; and a second valve disposed in the connection pipe.