Decaspirones F-H (1-3), three new spirobisnaphthalene derivatives, and one new non-spirobisnaphthalene, decaspirone I (4), have been isolated from cultures of an isolate of the saprophytic fungus Helicoma viridis. The structures of these compounds were determined mainly by analysis of their NMR spectroscopic data. The absolute configuration of decaspirone F (1) was established by X-ray crystallographic analysis of its mono-bromobenzoate derivative. In standard disk assays, compounds 1-4 showed modest activity against Pseudomonas aeruginosa (multiple antibiotic-resistant strain, ATCC 27853), and decaspirone G (2) also displayed activity against Lactococcus lacti (PCM 2379).