A heat conducting composite material includes a matrix and a graphene sheet. The graphene sheet has a two-dimensional planar structure, and a basal plane of the graphene sheet has a lateral size between 0.1 nm and 100 nm such that the graphene sheet has a quantum well structure. When radiation energy passes through the heat conducting composite material, the radiation energy is converted into infrared light by the quantum well structure of the graphene sheet to achieve high radiating efficiency. A light-emitting diode (LED) having the heat conducting composite material and capable of achieving a heat dissipation effect is further disclosed.