Angiogenesis is a critical step in tumor progression and involves several steps including endothelial cell (EC) proliferation, migration, and matrix remodeling. We investigated the antiangiogenic effects of 20( S)-protopanaxadiol ( 1) and 20( S)-protopanaxatriol ( 2), the sapogenins of two major ginseng saponins, in an angiogenesis model of human umbilical vein endothelial cells (HUVECs). These compounds inhibited the proliferative activity of HUVECs in a dose-dependent manner and have potential as anticancer drug candidates. In addition, we report the complete and unambiguous assignment of (1)H NMR spectra of 1 and 2, based on analyses of 2D NMR spectra including COSY, NOESY, HSQC, and HMBC. This report is the first to completely assign the (1)H NMR signals of 2, together with correction of data for 1 from prior reports.