The effects of carbon sources, seawater concentration and seawater component in a culture medium were investigated to optimize culture conditions for growth by a marine thraustochytrid Aurantiochytrium limacinum strain mh0186. Strain mh0186 could utilize D-glucose, D-fructose and D-mannose as carbon sources. Seawater concentrations between 12.5 - 200% were required for good growth, and a single omission of magnesium sulfate from the seawater reduced the growth of the cells. Jar fermentor trials were carried out for the purpose of docosahexaenoic acid (DHA) production by strain mh0186. The total fatty acid content of the cell was 466.5 mg/g dry cells, and biomass and DHA yield were estimated as 23.1 g/L and 4.3 g/L, respectively, at 26 h. The daily production of DHA by the strain was 4.0 g/L/d, suggesting that the higher DHA production rate of our strain mh0186 should be appropriate for industrial production of DHA.