The extract of the Indian green mussel (Perna viridis L.) was found to inhibit the formation of endothelial cell capillary tube in a concentration dependent manner in vitro. At a concentration of 5 mg/ml of crude extract, there no formation of intercellular junctions and capillary tubes was observed, even after 6 hours. However, at the concentrations below 1 mg/ml, a few cellular junctions and formation of capillaries began to increase at both concentrations of 0.2 and 0.04 mg/ml. The aqueous fraction was also found to inhibit the capillary and junction formations at 5 mg/ml, but it was less effective at lower concentrations, as compared to the total crude extract. The methanol (MeOH) extract was more active than that of the aqueous extract; hence, it was further fractionated into 5 fractions (F1 to F5) and tested for the presence of angiogenic activity. Fraction 3 (F3), which was used at 100 µg/ml concentration, showed a significant inhibitory effect on the formation of intercellular junctions and tube, whereas the other fractions did not show any activity.