Abstract: A natural occurring agglutinin, which was detected from serum of Spinibarbus sinensis, was found to have the ability of agglutinating different kinds of antigen. It has the characteristic of glycoprotein. The agglutinin was stable when exposured to the heat(60℃) for 1 h and acid (pH=2) or alkaline (pH=10) for 24 h,respectively, but was sensitive to the treatment of 1% -mercaptoethanol.Its agglutinating activity was influenced by the temperature, reaction time and concentrating of ion of PBS. The agglutinating activity could be inhibited by the splitting of lactose and sucrose. The results demonstrated the sugar referred above played an important role in agglutinating reaction.