A natural lectin from the seed of peanut Arachis hypogaea was purified by singlestep affinity chromatography using galactoside-coupled agarose. This lectin was named PN-L and its inactive form had a molecular mass estimate of 29 kDa. The lectin PN-L was detected for agglutinating activity, glycoinhibiting action and thermostability. The influence of pH on those activities was also tested. The results showed that PN-L could not agglutinate three kinds of human erythrocytes. But it showed a strong affinity for human A/B/O erythrocytes (RBC) by neuraminidase treated. Agglutinating activity of PN-L to neuraminidase treated human O erythrocytes was inhibited by lactose , raffinose, melibiose and D-galactose. The agglutinating activity of peanut seed lectin was inhibited at temperatures greater than 55 and at a pH less than 5 or greater than 11.