A new ganoderic acid (GA), 7-O-ethyl ganoderic acid O (GA-O) (1), together with two known compounds, GA-T (2) and GA-Me (3), was isolated and purified from fermented mycelia of Ganoderma lucidum. The structure of the new triterpenoid was elucidated on the basis of the interpretation of extensive spectroscopic data (HR-MS, IR, UV, 1D and 2D NMR) as 3,15,22-triacetoxy-7-ethoxy-5-lanost-8, 24E-dien-26-oic acid. The new compound was found to contain a rare ethoxyl group at C-7. In addition, its cytotoxicity against 95D and HeLa human cancer cell lines was also evaluated. © 2010 Taylor & Francis.