An LED lamp includes a heat sink including a base and a plurality of fins extending from the base, an LED module mounted on a bottom face of the base, an envelope covering the LED module, and a lamp housing defining a cavity. An annular receiving groove is recessed from the bottom face of the base. The LED module is attached on the bottom face of the base and surrounded by the receiving groove. The envelope includes a recessed body and an engaging flange around the recessed body. The heat sink, the LED module and the envelope are received in the cavity. The fins of the heat sink extend outwardly through the lamp housing and are exposed in an outer environment. A gasket is received in the receiving groove and tightly sandwiched between the base and the flange.