The internal friction of the Pb-Sn alloys was measured during heating process fr om room temperature to high temperature.It is reported that there is a sudden dr op in the internal friction curves of the vibration systems with the presence of solid-liquid transition of the Pb-Sn alloys.The decrement of the internal frict ion varies with the content of tin.It is proposed that these variations are rela ted with the structure variation of the Pb-Sn alloys during solid-liquid transit ion.