Five new oleanane-type triterpenoids were isolated from mastic. Their structures including absolute configurations were determined by extensive spectroscopic methods and single-crystal X-ray crystallographic experiments. Compound 1 is distinguished by its rare furan ring. Compounds 3-5 are formed by the oxidative ring-opening reaction of the A ring in oleanane-type triterpenes, while compounds 3 and 4 are nor-triterpenes with a carbon atom missing at the C-28 position. The anti-inflammatory potential of the compounds was anticipated through network pharmacology, followed by a detailed molecular docking analysis. Finally, the anti-inflammatory effects were verified through the establishment of an in vitro model. Notably, compounds 3 and 4 exhibited significant inhibitory effects on NO production in RAW264.7 cells induced by lipopolysaccharide, with IC