This project has been worked out for isolation of EPA-producing bacteria from marine source of sea water, sea sediment and intestinal contents eviscerated from some red-muscle fish such as mackerel, horse-mackerel and spike fish. The samples were precultured on the media of PPES-II glucose broth and then pure-cultured on Nutrient agar and P-Y-M glucose. Lipids extracted from those bacterial mass collected by centrifugation were analysed in terms of lipid class and fatty acid composition. The results are resumed as follows : 1. 112 strains from sea water and 76 strains from sea sediment were tested for their EPA producing capability, but both strains of (SA-67 and SA-91) from the former and four strains(SS-35, 37, 51 and 71) from the latter have been proved to produce EPA above the level of 2% of total fatty acids. The strains such as GS-11, 29, 31, HM-9, 29, B-18, 33, 107, YL-129, 156, 203, 77, 104 and 256 which were isolated from fish intestinal contents, have also produced EPA at higher level than 2% of total fatty acids. 2. Contents of total lipids extracted from the cultures of these strains grown at 25℃, range from 2.8% to 6.9% (on dry weight %), and they are mainly composed of polar lipids(40.9~52.9%) such as phosphatidyl glycerol(+cardiolipin)(?) and phosphatidyl ethanolamine (33.8~40.0%), with smaller amount of free fatty acid (11.2~20.2%). 3. EPA was isolated from a mixture of fatty acid methyl esters obtained from the lipid of each strain by HPLC in silver-ion mode and was identified by GC-Mass spectrometry. 4. The strains of SW-91, GS-11, GS-29, HM-9, B-18 and YL-203 grown at 25℃ have a level of 5% EPA in their total fatty acids, and the GS-11 and HM-9 strains show a tendency of increase in the EPA level with an increase of growth temperature.