An exemplary loop heat pipe includes an evaporator, a condenser, a vapor line and a liquid line each connecting the evaporator with the condenser to form a closed loop. A working medium is contained in the closed loop. A wick structure is received in the evaporator, and includes a bottom wall contacting the bottom plate, a support wall extending up from the bottom wall and contacting the cover plate, and guide walls extending out laterally from the support wall. The support wall separates an interior of the evaporator into a liquid chamber adjacent to the liquid line and a vapor chamber adjacent to the vapor line. The guide walls are located in the vapor chamber. Guide channels are defined between the guide walls for guiding the working medium in a vapor state to flow from the vapor chamber through the vapor line to the condenser.