By using hybridoma2monoclonal antibody technology , thirteen hybridoma cell lines which secrete monoclonal antibodies (Mab) against the IgM of European eel (Anguilla anguilla) had been established. And the characteristics of these Mabs had been described. In isotyping analysis , the results showed that among these Mabs , three of them are IgM , five of them are IgG1 , three of them are IgG2a and two of them belong to IgG2b ; all of these Mabs have the ability to bind the eel IgM by ELISA and their titer ranged from 104 to 107 , seven out of thirteen Mabs are able to recognize the heavy chain of the IgM on western blot. Further experiments proved that all of them only specifically bound to Ig of European eel and Japanese eel , and did not have any cross reaction with the Ig of Crucian carp 、Colossoma brachypomum cuvier 、Tilapia 、Clarias f uscus 、Ictalurus punctatus , and also did not react to the fish common bacterial pathogen , such as Aeromonas 、Edwardsiella 、Vibrio 、Flexibacter columnaris 、Salmonella and Escherichia coli . The measuring sensitivity of the Mab MaE9D7 to purified eel IgM was as low as 16ng. All of these results demonstrated that Mabs were highly specific and sensitive to the Ig of European eel , and had the great potential to be used for analyzing the structure of eel IgM , monitoring the immunity level of cultured eel , and pathogen diagnosis .