A new lectin was purified from Bombyx mori (BML) by physiological saline extraction, ammonium sulfate precipitants, anion exchange column chromatography on DEAE Sephadex A-50 and gel filtration column chromatography on Sephadex G-200. BML agglutinated trypsinized and glutaraldehyde-fixed erythrocytes, and was observed the most high activity with rabbit, chicken erythrocytes and rat splenic lymphocytes. Agglutinability was markedly affected at highly acidic pH, but was relatively stable with high temperature. The effect of metal ions was observed and BML was affected by bivalaent cations, especially depending on $Ca^{2+}$, $Fe^{2+}$, $Mn^{2+}$, whereas, inhibited by $Mg^{2+}$. Agglutination was strongly inhibited by heparin and glucuronic acid. BML was proved to be a glycoprotein which contains 17.16% of sugars. By mass spectrometry analysis, we found 2 bands that were considered as lectin subunits.