The ethyl acetate fraction of Bupleurum longiradiatum was found to have an inhibitory effect on the tube-like formation of human umbilical venous endothelial (HUVE) cells. The active compounds, isolated from the fraction, were identified as acetylbupleurotoxin (P1) and bupleurotoxin (P2). The compounds P1 and P2 completely inhibited the tube-like formation of HUVE cells at 30 ${mu}g$/ml, below the cytotoxic concentration. But, they did not exhibit antitumor activity on BDF1 mice bearing Lewis lung carcinoma cells despite their antiangiogenic activity.