The degree of offensive odor of decoyed eels cultured in the sea water along Mizushima industrial area was studied and offensive odor substance in decoyed eels was analyzed by gas chromatography. The results obtained were as follows. Ninety percent of decoyed eels changed into offensive odor eels when cultured in the sea water within a distance of 1km. from the exit of industrial waste. Offensive odor of decoyed eels is similar to that of offensive odor fish caught in this sea and new peak considerd to be offensive odor substances was revealed in gas chromatogram with gas evaporated from offensive odor eels. This new peak is corresponded to tha peak with sea water and that with industrial waste. Degree of offensive odor and also offensive odor peak in gas chromatogram were scarcely found in the eels cultured in the sea at a very distanee of about 1Km. from the harbor. From decoyed eels or odor-substances in the sea-water, it was recognized that fishes which had lived north in Mizushima harbors became gradually evil-odor fishes in various degrees corre sponding to degree of odorness and quantity of odor-substances in the sea-water.