OBJECTIVE: To study the chemical constituents of the EtOAc extract of Armillaria gallica 012m. METHODS: The chemical constituents of the EtOAc extract of A. gallica 012m were isolated and purified by various column chromatography and their structures were elucidated on the basis of the 1D and 2D NMR spectroscopic and HRESIMS data. Cytotoxicity of all isolates against A549, HCT-116, M231 and W256 human tumor cells was determined by the MTT method. RESULTS: A new sesquiterpene aryl ester, armimelleolide C ( 1), and eight known ones including armillarivin ( 2), melleolide F ( 3), 6'-chloromelleolide F ( 4), melleolide ( 5), melleolide K ( 6), melledonol ( 7), 13-hydroxydihydromelleolide ( 8), and armillane ( 9), were isolated from the EtOAc extract of A. gallica 012m. All isolates showed potential cytotoxic activities against at least one of the human cancer cell lines with IC₅₀ values ranging from (3.17 ± 0.54) to (17.57 ± 0.47) μmol/L. Compound 1 showed significant inhibitory activity against M231 with an IC₅₀ value of (7.54 ± 0.24) μmol/L compared with paclitaxel as the positive control. Compounds 2, 3, and 7, 9 showed obvious inhibitory activity against HCT-116 and were better than that of the positive control. CONCLUSION The chemical constituents including a new sesquiterpene aryl ester armimelleolide C ( 1) from the EtOAc extract of A. gallica 012m have a variety of structures and potential antitumor activities.