Talaronoids A-D (1-4), four diterpenoids with an unexpected tricyclic 5/8/6 carbon skeleton isolated from Talaromyces stipitatus, represent a new class of fusicoccane diterpenoids and the first examples of natural products with a benzo[a]cyclopenta[d]cyclooctane skeleton. Their structures were established by a combination of extensive spectroscopic analyses and electronic circular dichroism spectral calculations. Plausible biosynthetic pathways of 1-4 are proposed starting from geranylgeranyl diphosphate with a Wagner-Meerwein rearrangement as the key step. Compounds 1-4 were evaluated for butyrylcholinesterase inhibitory activity in vitro, and compounds 1-4 showed moderate activity.