Ag-decorated multi-walled carbon nanotubes (Ag-MWCNT) were investigated for use in Sn58Bi solder joints for FCLED packages. Among lead-free solders, Sn58Bi solder has been identified as a candidate for widespread use because of its low melting temperature and high tensile strength. However, Sn58Bi solder is brittle, and it is difficult to relieve it from an impact shock. To overcome these limitations, the bonding characteristics of Sn58Bi solder have been improved with Ag-MWCNT. Ag-MWCNT composite solder paste is fabricated by mixing Ag-MWCNTs of various concentrations with solder paste, and the FCLED chips are bonded on the printed circuit board. The thermal, electrical, and mechanical properties of the solder joints are investigated using various tests. The bonding strength of the Sn58Bi solder with the Ag-MWCNTs increased by 16% compared to that without it. Furthermore, the thermal resistance of the solder alloy decreased by a factor of 2 with the addition of 0.1 wt% Ag-MWCNT.