Ten terpenes (1-10), two sterols (11 and 12), and two unusual phenylpropanoids (13 and 14) were isolated from the brittle star Ophioplocus japonicus (Family Ophiuridae). Their structures were identified by analyses of the spectral data and by comparison with the literature data. The terpenes (1-10) and phenylpropanoids (13 and 14) are first encountered in brittle stars. These compounds were evaluated for cytotoxicity against a small panel of human solid tumor cell lines. Compounds 6-10 and 14 displayed moderate to significant cytotoxicity. The compounds were evaluated for antibacterial activity against 20 clinically isolated strains. Compound 5 exhibited antibacterial activities against three Streptococcus and three Staphylococcus strains.