To search new sources of lectin, an experiment on lectin distribution in humoral serum of crab Charybdis feriatus (in short, CFL) was conducted March, 2002. When adding solid ammonium sul-fate into the fluids up to 50% saturation at 4℃, most CFL activity showed precipitates who were then continually extracted by ammonium sulfate of different concentrations. The supernatant, which was called primary CFL fluids, was given a 17.60-fold purification and 45.70% recovery of total activity. Finally, by using Sephadex G-100 column chromatography, the CFL in the primary CFL fluid was highly purified. Compared to the original humoral fluids, the last purified CFL got a 203.90-fold purification and 30.48% recovery of total activity, and demonstrated a single band on SDS-PAGE. In the same time, the purified CFL was detected for agglutination activity with 7 kinds of animal erythrocytes. Other characterization, such as sugar inhibition, and the effect of temperature on the agglutination activity of CFL were also studied. Our results indicate that agglutination activity of CFL was influenced by sugar and temperature. To search for new sources of lectin, an experiment on lectin distribution in humoral serum of crab Charybdis feriatus (in short, CFL) was conducted March, 2002. When adding solid ammonium sulphate to the fluids up to 50% saturation at 4 ° C, most CFL activity showed precipitates who were then continually extracted by ammonium sulfate of different concentrations. The supernatant, which was called primary CFL fluids, was given a 17.60- fold purification and 45.70% recovery of total activity. Finally, by using Sephadex G-100 Compared to the original humoral fluids, the last purified CFL got a 203.90-fold purification and 30.48% recovery of total activity, and demonstrated a single band on SDS-PAGE. In the same time, the purified CFL was detected for agglutination activity with 7 kinds of animal erythrocytes. Other characterization, such as sugar inhibition, and the effect of temperature on the agglutination activity of CFL was also by studied. Our results indicate that agglutination activity of CFL was influenced by sugar and temperature.