Five new 20-nor-isopimarane diterpenoids, aspewentins D-H (1-5), along with a related known congener, aspewentin A (6), were isolated from the culture extract of Aspergillus wentii SD-310, a fungal strain obtained from a deep-sea sediment sample. The structures of these compounds were established on the basis of spectroscopic interpretation, and the absolute configurations of compounds 1-5 were determined by X-ray crystallographic analysis and TDDFT-ECD calculations. The isolated compounds were evaluated for antimicrobial activity against nine human and aquatic pathogenic bacteria and four plant pathogenic fungi as well as for lethality against brine shrimp (Artemia salina). 20-Nor-isopimarane derivatives rarely occur in fungi, and only three (aspewentins A-C) have previously been reported from a marine-derived fungus.