Flip-chip light-emitting diode (FCLED) packages were interconnected with various contents of Sn-decorated multi-walled carbon nanotube (Sn–MWCNT) composite solder. The Sn–MWCNT was synthesized with a Sn solution using polyol to decorate Sn nanoparticle on the surface of MWCNTs. The Sn-58Bi solder pastes containing Sn–MWCNTs were printed on the metal-printed circuit boards, and then bonded with a flip-chip bonder. The mechanical property of FCLED packages with various contents of Sn–MWCNTs were evaluated with a bond tester. Thermal property was measured with IR Camera and laser flash analysis. The shear strength of an LED chip with 0.1 wt% Sn–MWCNT solder increased about 25% over that without Sn–MWCNT. The LED chip temperature with 0.1 wt% Sn–MWCNT nanocomposite solder decreased about 7% compared to that of the Sn-58Bi solder.