A heat dissipating device includes a heat dissipating block, a liquid contained in the heat dissipating block, a first conduit joined to one end of the heat dissipating block, a second conduit joined to the other end of the heat dissipating block, a guiding tube, heat dissipating fins on the guiding tube, and a fan right above the heat dissipating fins; both the conduits communicate with the inside of the heat dissipating block; the guiding tube is connected to and communicates with the first and the second conduits at two ends so as to slope; the heat dissipating device is secured in position with the heat dissipating block closely touching an upper side of a CPU; therefore, the heat dissipating device will dissipate heat produced by the CPU with the fan producing wind to carry away heat carried to the heat dissipating fins and the liquid repeating a vaporization-condensation cycle.