Abstract: This work aims to establish an expeditious method of mutation breeding strain producing high-yield docosahexaenoic acid（DHA）. The original strain Schizochytrium sp. ATCC 20888 was treated by Atmospheric and Room Temperature Plasmas（ARTP）, and screened with 100% lethal concentration of 2, 2&-Dipyridyl. The mutants were cultured by rotation-flask fermentation, and the strains with high-yield DHA from mutants were screened and selected by phosphoric acid-vanillin reaction and gas chromatography. The results showed that the conditions of mutation breeding Schizochytrium were ARTP for 15 s at the gas flow rate of 10.0 L/min and radio-frequency output of 100 W, and the concentration of 2, 2&-Dipyridyl was 100 μmol/L, so the strain with high-yield was obtained. The DHA-yield of mutant D32 increased significantly up to 7.31g/L, 29.8% higher than those by the original strain. Compared with the original strain, the main saturated fatty acid（C14:0 and C16:0）by D32 decreased significantly（P < 0.005）, while the unsaturated fatty acid content increased significantly（P < 0.005）. The results of subculture test showed that the mutant strain had stable hereditary character after 5 generations. Therefore, this method is not only prompt and efficient, but also provides a reference for the mutation breeding strains of producing other polyunsaturated acids.

Key words: DHA, Schizochytrium, mutation breeding, atmospheric and room temperature plasmas