A waterproof heat dissipating structure is provided on an electronic signboard having a main body with a first surface as a display and an opposite second surface, and includes at least one through hole provided on the second surface of the main body of the signboard, and at least one waterproof breathable unit provided at each through hole as a protective layer. The waterproof breathable unit has an area not smaller than that of the through hole, and has the property of allowing gas but not liquid to pass therethrough. Therefore, air inside the main body heated by the heat produced by the display at the first surface of the signboard may pass through the waterproof breathable unit at the through hole to carry away heat from the main body to achieve the purpose of heat dissipation and maintain the main body at a pressure balancing state.