Two new bicyclic polyketide lactones, polyrhacitides A ( 1) and B ( 2), were isolated from Chinese medicinal ants, Polyrhacis lamellidens, which have been used as an effective therapeutic agent to treat rheumatoid arthritis and hepatitis in China. Their absolute structures were elucidated on the basis of spectroscopic analyses and chemical evidence. The occurrence of polyketides with similar structures in plants of the Lamiaceae, Lauraceae, and Staphyleaceae indicates their significance in the study of chemical ecology.