Lectin from green marine algae Enteromorpha intestinalis (EIL) was isolated by extraction with PBS, followed by ammonium sulfate fraction and a combination of ion-exchange chromatography on DEAE-52 fiber and gel filtration on SephadexG-200. Lectin showed single band on both PAGE and isoelectrofocusing electrophoresis. Its isoelectric point was 8.9 and molecular weight was 17783 tested on SephadexG-200. EIL displayed some agglutination activities with Chlamydomonas and erythrocytes of rabbit, common carp, crucian carp and human (A, B, AB, O), but the maximum agglutination was with crucian carp. The hemagglutinating activity for rabbit erythrocyte could not be inhibited by D-fructose, D-galactose, glucose, sucrose, mannose, lactose, bovine-thyroglobulin, egg albumin and gamma-globulin. The hemagglutinating activity of lectin would be showed at pH 4.0~10.2, and more potent at pH 6.9~8.0. The hemagglutinating activity was not affected at 90℃ for 1h, so it could be said that the lectin had high heat resistance.