Three new naphthoquinone derivatives, 6-(1-ethoxyethyl)plumbagin (16), ethylidene-3,3'-biplumbagin (17), and ethylidene-3,6'-biplumbagin (18), were isolated, in addition to six known naphthoquinones, isozeylanone (10), 3,3'-biplumbagin (11), chitranone (12), methylene-3,3'-biplumbagin (13), 2,3-epoxyplumbagin (14), and 3,8'-biplumbagin (15), from the fruits of Diospyros maritima Blume (Ebenaceae). The structures of the new compounds were established by spectroscopic methods. The eight naphthoquinones 11-18 were examined for ichthyotoxic activity and germination inhibitory activity. The quinones 11, 12, and 14-16 showed strong ichthyotoxic activity and the quinone 14 mild germination inhibitory activity.