Edwardsiella tarda, the causative organism of Edwardsiellosis, was isolated from the water and the eel, Anguilla japonica of the recirculating eel culture ponds in 1988. E. tarda was always isolated from the water of eel culture ponds in the number of log 2.30~log 4.78 CFU/$m{ell}$ without distinguishable seasonal characteristics. The counts of isolated E. tarda were changed with the health condition of the eel, i. e., a number of E. tarda were isolated from all checked organs, intestine contents, liver, spleen and kidney of the diseased eel, however, it was hardly isolated from spleen and kidney of the healthy eel. The isolates were classified according to o-agglutinating test into three serotypes (I, II, III). There were no distinct differences in the composition of the serotypes between intestine contents of eel and pond water samples(I, 52.4~53.3% ; II, 20.0~23.8% ; III, 4.8~6.7%). Serotype I was ascendant in the spleen(66.7%) and the kidney(73.7%) samples. By experimental challenge, most of serotype I proved highly virulent to eel in comparison with the other serotypes tested.