Abstract: The lectin from brown algae Undaria pinnatifida was isolated by extraction withTBS, followed by 50% ammonium sulfate fractionation. The lectin was purified by 7.7 times,and had 167% recycle - rate. It contained 5. 72% of sugar in crude extract. The hemaggluti-nating activity for rabbit could not be inhibited by D -fructose, glucose, gamma - globulin (hu-man). This lectin had the maximum hemagglutinating activity at pH 5. 0 ~9. 51, with activityat pH 4. 0~10. 14.