Twelve new highly oxygenated lanostane triterpenoids and nine known ganoderic acids were isolated from the fruiting body of Ganoderma lucidum. The new compounds were lanostane nortriterpenoids with 27 carbons (1-5 and 8), lanostane nor-triterpenoids with 25 carbons (6 and 7), and lanostane triterpenoids (9-12) based on multiple spectroscopic data analysis, including HRESIMS, 1D-NMR, 2D-NMR, and CD. Compounds 1-5 were identified as rare nor-lanostanoids that contain a 17β-pentatomic lactone ring. Compound 13, possessing a lactone ring, had been isolated previously. The P-glycoprotein (P-gp) inhibitory effects of compounds 1-21 were evaluated at a concentration of 20 μM using an adriamycin (ADM)-resistant human breast adenocarcinoma cell line (MCF-7/ADR). Compounds 1, 5, 18, and 20 and verapamil increased the accumulation of ADM in MCF-7/ADR cells approximately 3-fold when compared with the negative control. These data support the significant P-glycoprotein inhibitory activities of compounds 1, 5, 18, and 20. In silico docking analysis suggested these compounds had similar P-gp recognition mechanisms compared with those of verapamil (a classical inhibitor). Furthermore, in an in vitro bioassay, compounds 2, 4, 5, 6, and 18 showed moderate inhibitory effects against α-glucosidase compared with those of the positive control acarbose.