Dehydroxychlorofusarielin B (1), a new antibacterial polyoxygenated decalin derivative, and the previously described fusarielins A (2) and B (3) have been isolated from the broth of a marine isolate of the fungus Aspergillus. The structure and absolute stereochemistry of the new compound was determined on the basis of the physicochemical data and X-ray diffraction. Compounds 1-3 exhibited a mild antibacterial activity against Staphylococcus aureus, methicillin-resistant S. aureus, and multidrug-resistant S. aureus. The MIC values for each strain were as follows: compounds 1 and 3, 62.5 microg/mL for all strains; compound 2, 32.5 microg/mL for S. aureus and methicillin-resistant S. aureus and 62.5 microg/mL for multidrug-resistant S. aureus.