Bi-Sn-Zn is one of the systems being used as substitute of the traditional lead solders. Therefore a deeper knowledge of its phase diagram is a priority. Due to the lack of data about the thermodynamic properties of terminal solid solutions as well as on their phase boundaries, only binary contributions were utilized and the ternary terms were ignored on the published assessments [1, 2]. Samples corresponding to several vertical sections were prepared and DTA, SEM/EDS and XRD at room and high temperatures were performed. It was concluded that ternary terms should be held in consideration in a future assessment of the system.