An LED lamp includes a heat sink (10) and a plurality of LED modules (20) mounted on a periphery of the heat sink. The heat sink defines a through hole (122) from a lateral side to an opposite lateral side thereof to define a cylindrical inner face. A plurality of fins (16) are attached to the heat sink in a manner such that the fins have spaced external portions (160) extending outwardly from the periphery of the heat sink, and opposite internal portions (162) extending inwardly from the inner face of the heat sink. The internal portions connect with each other to form a joint (164) in the through hole, thus increasing a heat dissipating area of the heat sink and reinforcing the heat sink.