The chemical investigation of the crude extract of the marine-derived Streptomyces sp. M491 yielded three new sesquiterpenes, namely, 10alpha,11-dihydroxyamorph-4-ene (4), 10alpha,15-dihydroxyamorph-4-en-3-one (6), and 5alpha,10alpha,11-trihydroxyamorphan-3-one (7). In addition, the known compounds 10alpha-hydroxyamorph-4-en-3-one (2), o-hydroxyacetanilide, genistein, prunetin, and indole-3-carbaldehyde and the macrolide antibiotic chalcomycin A were identified. The structures were determined on the basis of spectroscopic analysis, especially 1D and 2D NMR data. This is the first report of these sesquiterpenes from bacteria.