A new antiangiogenic compound, bryoanthrathiophene (1), together with two known compounds, 5,7-dihydroxy-1-methoxycarbonyl-6-oxo-6H-anthra[1,9-bc]thiophene (2) and 1,8-dihydroxyanthraquinone (3), was isolated from the bryozoan Watersipora subtorquata (d'Orbigny, 1852) using bioassay-guided fractionation methods. Among them, bryoanthrathiophene (1) exhibited the most potent antiangiogenic activity on BAEC (bovine aorta endothelial cell) proliferation.