A heat exchanger includes a body having a center and a spiral guiding trough extending spirally and outwardly from the center toward an outside of the center. The radius of the spiral guiding trough increases gradually from the center toward the outside of the center. A first port and a second port are in communication with the spiral guiding trough respectively. With the combination of the spiral guiding trough and the body, the fluid can be sufficiently mixed in the spiral guiding trough, thereby achieving an excellent thermal-conducting effect.