This work investigates the effect of Indium (In) addition, 0.5 wt.% In, on the wettability of the Sn-3Ag-0.5Cu (SAC305) ternary pb-free solder alloy. Adding In to SAC305 decreased the contact angles (.) of the Sn-2.5Ag-0.5Cu-0.5In quaternary pb-free solder alloy decreased which were measured by using of the sessile drop method at various temperatures (250, 280 and 310 degrees C) on Cu substrate in Ar atmosphere. Microstructures, inter-metallic phases, and melting temperatures of alloys were characterized by optic microscope and scanning electron microscope and energy dispersive X-ray spectroscopy, X-ray diffraction, and differential scanning calorimeter, and effects of the amount of In on microstructure were investigated. The results indicated that when the addition of In was 0.5 wt.%, the change in melting temperature of Sn-2.5Ag-0.5Cu-0.5In solder was negligible, but the contact angles (.) of the solder alloy decreased which were measured by using of the sessile drop method at various temperatures. The lowest. was obtained as 45.22 degrees for Sn-2.5Ag-0.5Cu0.5In alloy at 310 degrees C. The formation of intermetallic compounds (IMC) between the Pb-free solder alloys and the Cu substrate was observed. Thus, If the amounts of indium and silver are optimized, the Sn-2Ag-0.5Cu-0.5In quaternary solder alloy may be a suitable potential candidate to replace conventional Sn-3.0Ag-0.5Cu solder to provide economic gain in solder alloy production.