Four novel globostellatic acid X methyl esters (1-4) having isomarabarican-type triterpenoidal skeleton and three related new compounds (5-7) were isolated from the marine sponge Rhabdastrella globostellata, as selective anti-proliferative agents against human umbilical vein endothelial cells (HUVECs). Those chemical structures were elucidated by the detailed 2D NMR analysis. Two globostellatic acid X methyl esters (3 and 4) having 13E-geometry were found to inhibit proliferation of HUVECs, 80- to 250-fold selectively in comparison with several other cell lines. 13E,17E-Globostellatic acid X methyl ester (4) also inhibited bFGF-induced tubular formation and VEGF-induced migration of HUVECs. Moreover, 4 induced apoptosis of HUVECs, whereas it exhibited no effect on VEGF-induced phosphorylation of ERK1/2 in HUVECs.