Phytochemical investigation of mastic, a resin produced by Pistacia lentiscus, led to the isolation and identification of 16 tirucallane triterpenoids, 13 (1-13) of which are undescribed. Their structures and absolute configurations were elucidated based on the analysis of spectroscopic data and single-crystal X-ray diffraction. Compounds 12 and 13 are unusual 7(8 -> 9)abeo-tirucallane triterpenoids. Anti-inflammatory assays indicated that compounds 7, 8, 14, and 16 exhibited stronger inhibitory NO production activities (IC50 = 7.7-13.4 mu M) than that of the positive control dexamethasone (IC50 = 19.5 mu M). In addition, compound 1 showed comparable cytotoxic activity against HepG2 cells to that of doxorubicin (IC50 = 4.92 VS 1.34 mu M).