Abstract: Several colonies of Flexibacter were found on the Menkina media (organic or inorganic phosphate medium) from sediment samples of Donghu Lake. They have the ability to decompose organic substances. It seems that Flexibacter is one of the important bacterial groups in the aquatic ecosystem. The Menkina media can be used for Flexibacter isolation and cultivation. The biological characters (including morphological, physiological and biochemical characters) of four representative strains of Flexibacter isolated from Station Ⅰ and Ⅱ in Donghu Lake were examined and compared with the type strains of Flexibacter chinensis, F. canadensis and F. pinensis using a microcomputer. Cluster analysis indicated that the similarity between F875 and F877 is rather high (similarity value 0.80) the similarity value between the four representative strains and F. chinensis FCA is 0.75. The four strains were considered as different physiological strains of F. chinensis. The similarity value between F. canadensis Fxcl and F. pinensis Ctpl strains is 0.65. All strains can be clustered in to one group at a similarity value of 0.61. These results are consistent with the results obtained by traditional classification methods.