A novel hirsutane-type sesquiterpene with unprecedented modification of the hirsutene scaffold, lentinulactam (1), along with four known metabolites, connatusin A (2), connatusin B (3), 6-hydroxy-2,2 dimethylchroman-4-one (4), and 6-methoxy-2,2-dimethylchroman-4-ol (5) were obtained from the cultures of the basidiomycete fungus Lentinus cf. fasciatus. The absolute configuration of compound 1 was determined on the basis of the NMR spectroscopic data and Mosher ester analysis. The isolation, structure elucidation, and biological evaluation are reported. Lentinulactam (1) is the first hirsutane-type terpenoid containing unusual modification of the hirsutene scaffold represented in 5-6-6 tricyclic skeleton and the bridged lactam ring with an exocyclic double bond. Moreover, lentinulactam (1) represents the first member of hirsutane family having the opposite absolute configuration to those determined for other hirsutanes.