In the quest for medicinally active compounds in mushrooms of the genus Ganoderma, eleven undescribed lanostane triterpenoids, including a novel chlorinated derivative, i.e., (20S,24E)-21-chloro-15β,20,29-trihydroxy-3,7,11-trioxolanosta-8,24-dien-26-oic acid, were isolated from artificially cultivated fruiting bodies of the basidiomycete Ganoderma mbrekobenum. The structures were elucidated on the basis of NMR spectroscopic and mass spectrometry data. The configuration of the C-20 atom in the most abundant 20-hydroxy-lanostane, (20S,24E)-15β,20,29-trihydroxy-3,7,11-trioxolanosta-8,24-dien-26-oic acid, was established by chemical derivatization, and the absolute configuration of the lanostane skeleton was determined by ECD calculation. Two of the undescribed compounds exhibited moderate antimalarial activity.