Three novel anti-angiogenic steroidal alkaloids, cortistatins J (1), K (2), L (3), have been isolated from the Indonesian marine sponge Corticium simplex. The chemical structures of cortistatins J (1), K (2), and L (3) were determined by 2D-NMR analysis to be unique abeo-9(10-19)-androstane-type steroidal alkaloids having isoquinoline unit instead of the side chain part, respectively. Cortistatin J (1) showed cytostatic anti-proliferative activity against human umbilical vein endothelial cells (HUVECs) at 8 nM, in which the selective index was 300-1000-fold in comparison with other cell lines. © 2007 Elsevier Ltd. All rights reserved.