The Sn-base Pb-free solder alloys are candidates for replacement of widely used Pb-Sn solders. To select a proper Pb-free solder alloy system, informations on binary and ternary phase diagrams are required. As a part of ongoing program on alloy designes of Pb-free solder systems, thermodynamci reassessments of Bi-Sn and In-Bi systems have been made. For the binary Sn-In system, thermochemical calculations have been carried out to obtain relevant thermodynamci interaction parameters. Thermodynamic informations on these three binary systems were usde to extend to the calculation of Sn-In-Bi ternaruy system of interest. And, it was confirmed by DSC measurements.