ETHNOPHARMACOLOGICAL RELEVANCE: Cichorium intybus is a traditional medicinal herb for hepatitis treatment in China and Europe. Sesquiterpene lactones are the main active ingredients in C. intybus. However, their structure-activity relationship (SAR) and molecular mechanisms of anti-inflammatory and hepatoprotective effects require further elucidation. AIM OF THE STUDY: To identify new sesquiterpene lactones from C. intybus, and further evaluate their anti-inflammatory effects, SAR, and mechanisms of anti-inflammatory and hepatoprotective properties. METHODS: Identification of sesquiterpene lactones from C. intybus using chromatographic fractionation, NMR, and mass spectrometry. The repression of inflammation was evaluated in RAW264.7 macrophages incubated with LPS. Western blotting was employed to investigate the anti-inflammatory mechanisms. The hepatoprotective effect was measured in LPS/D-galactosamine (D-GalN)-induced acute hepatitis in mice. RESULTS: We identified 3 new sesquiterpene lactones and 15 known analogues from C. intybus. SAR analysis showed that the α-methylene-γ-lactone moiety was essential for their anti-inflammatory properties. Furthermore, 8-deoxylactucin was identified as the most potent anti-inflammatory component in LPS-induced RAW264.7 macrophages by reduction of nitric oxide production via inhibiting iNOS expression, and suppression of IL-1β, IL-6, and TNF-α expression. Mechanistically, 8-deoxylactucin not only blocked LPS-induced IKKα/β phosphorylation, IκBα phosphorylation and degradation, and NF-κB nuclear accumulation, but also enhanced NRF2 expression and nuclear translocation, HO-1 and NQO1 expression, and reduced ROS generation in vitro. In vivo, 8-deoxylactucin mitigated LPS/D-GalN-induced acute hepatitis, which manifested as reduction in inflammatory infiltration, live injury, serum levels of AST and ALT, and production of pro-inflammatory cytokines and 4-hydroxynonenal. CONCLUSION: 8-Deoxylactucin, the sesquiterpene lactone isolated from C. intybus, exerted anti-inflammatory and hepatoprotective effects by blocking NF-κB activation and enhancing NRF2 activation.