Two novel 3,4- seco-25,26,27-trinorlanostane triterpenoid compounds, fornicatins A and B ( 1 and 2 ) have been isolated from the fruiting body of Ganoderma fornicatum. The structural elucidation of 1 and 2 were accomplished by extensive NMR analysis. The relative stereochemistry of 2 was established by single crystal X-ray crystallography, which also confirmed the novel carbon skeleton of the new triterpenoid. An ether linkage of C-4 with C-7 in 1 is unprecedented in natural triterpenoids. Both compounds were tested for their inhibitory effects on rabbit platelet aggregation induced by PAF, ADP, or AA.