An LED lamp includes a support, an envelope, a heat sink assembly and a plurality of LED modules. The envelope is coupled to the support. The heat sink assembly includes a first heat sink mounted on the envelope, a cylindrical second heat sink attached to a bottom surface of the first heat sink and positioned in the envelope, and a plurality of heat pipes. The LED modules are mounted on an outside wall of the second heat sink. The heat pipes have condensing portions embedded in the bottom surface of the first heat sink and evaporating portions sandwiched between the outside wall of the second heat sink and the LED modules.