A light-emitting diode (LED) lamp and a polygonal heat-dissipation structure thereof are provided. The LED lamp includes a polygonal heat-dissipation unit and a lighting module. The polygonal heat-dissipation unit has a polygonal hollow column and fins. The fins and the lighting module are thermally disposed on an inner surface and an outer surface of the polygonal hollow column, respectively. Thus, heat generated by the lighting module is dissipated by the fins rapidly. As the fins are thermally disposed on the inner surface of the polygon hollow column instead of being exposed, the volume of the LED lamp can be minimized, and the look of the LED lamp also can be prettified.