Abstract: A heat-radiating device with a guide cap includes a radiator, a fan and a guide cap over the fan. The radiator is fixed to a circuit board by using four fixing bolts mounted in four corners of its bottom to attach tightly with a top surface of an electronic element. The guide cap is a quadrate frame and in the middle of each of its four side walls protrudes outward an arc surface, the four arc surfaces form by means of surrounding a truncated-cone shaped air flow path with a large upper and a small lower, in each of four corner of bottom of the guide cap provides a lock hole and protrudes downward four barbs for buckling with the hooks of the fan. The guide cap can feed effectively a low temperature air flow to improve the radiating efficiency of the radiator. In addition, configuration of the guide cap is easy to screw the four fixing bolts so as to assemble the heat-radiating device to a circuit board, and thus the assembling is more convenient.