In this study, ten undescribed norsesquiterpenoids, named marasmiellactones R−U (1−4) and marasmielolic acids A−F (5−10), were isolated from the cultures of the fungus Marasmiellus candidus. Their planar structures were characterised using comprehensive spectroscopic techniques, including 1D/2D NMR and HRESIMS, while the absolute configurations were determined by comparing experimental and calculated ECD spectra. In addition, the anti-inflammatory activities of isolated compounds were evaluated by using an LPS-induce RAW 264.7 cell model. Compounds 1−4 demonstrated good anti-inflammatory activity, with IC₅₀ values of 18.2, 16.7, 22.1, and 15.5 μmol/L, respectively.