Abstract: Liquid lead-bismuth alloy has been considered as the potential candidates for the liquid spallation targets and the coolant of accelerator driven sub-critical system (ADS). Surface tension is one of the important thermal and physical properties parameters of lead-bismuth alloy, and temperature and chemical composition are important influence factors of surface tension. In this paper, the surface tension of liquid lead-bismuth alloy was measured by sessile drop (SD) method. The results indicate that the surface tension of lead-bismuth alloy firstly increases and then decreases with the increase of the test temperature, and the surface tension for low test temperature is significantly small. At the same temperature, the surface tension of lead-bismuth alloy decreases with the increase of bismuth content, and segregation of bismuth onto the surface of molten lead-bismuth alloy is a key factor leading to the smaller surface tension. The results of this study provide basic reference for composition optimization of lead-bismuth alloy, which is of great significance for the development of spallation targets and the coolant materials of accelerated driven sub-critical system.