The typical morphology of metal lead (Pb) in ancient bronzes made in the Spring-Autumn Warring States Period (770 B.C. –221 B.C.), China, was examined by using electron microscopic techniques. We propose that the main purposes for adding metallic Pb in a large quantity into ancient bronzes such as arrows and ritual vessel-Ding were for increasing weight and economical reasons. SEM observations from the fracture surface of the bronzes revealed that the Pb particle possessed a “hollow–cored bubble” structure, which was formed due to absorbing casting gases during solidification and therefore indirectly eliminated the casting porosity and loosen.