One or more embodiments of the present invention relates to a heat exchanger. The heat exchanger comprises a pair of header-tanks having at least one partition wall and at least one baffle; a plurality of tubes; and a plurality of fins. A communication hole is formed on the partition wall that is positioned at a region disposed between the baffle and one end of the header-tank adjacent to the baffle. Given that a distance from the baffle to the one end of the header-tank is 100%, 1˜4 communication holes are formed at positions on the partition wall which corresponds to an extent of 0˜50%, 65˜100%, or an extent of 0˜50% and an extent of 65˜100%.