Meroterpenoids, meroindenon (1) and merochlorins E (2) and F (3), were isolated from a marine-derived bacterium belonging to the genus Streptomyces. Their chemical structures were established using extensive analysis of MS, UV, ECD, and NMR spectroscopic data. Compounds 1-3 possess a tetrahydroxynaphthalene core and a C15-isoprene unit. Compounds 2 and 3 exhibited strong antibacterial activities against B. subtilis, K. rhizophila, and S. aureus, with a range of MIC values from 1 to 2 μg/mL.