The whole plant of Sedum lineare Thunb has been used as traditional folk medicines for the treatment of sore throat, persistent hepatitis, jaundice and dysentery. δ-Amyrone (13(18)-Oleanen-3-one), a pentacyclic triterpene compound from S. lineare Thunb, was found to possess a potent anti-inflammatory effect in different inflammation model animals. Pretreatment with δ-Amyrone (i.p.) inhibited the ear edema in xylene-induced mouse ear edema. δ-Amyrone also decreased the level of nitric oxide (NO), prostaglandin E2 (PGE2), interleukin-6 (IL-6) and leukocyte numbers in acetic acid-induced peritonitis in vivo. To clarify the possible mechanism of δ-Amyrone, we investigated the effect of δ-Amyrone in lipopolysaccharide (LPS) induced peritoneal macrophages. The data indicated that δ-Amyrone notably inhibited IL-6, TNF-α and NO production. In addition, the result showed that δ-Amyrone may control the cyclooxygenase-2 (COX-2) regulation and not the cyclooxygenase-1 (COX-1) at protein levels. These results suggest that δ-Amyrone is a bioactive agent which possesses anti-inflammatory effects, which may be relevant to the regulation of COX-2.