Abstract: In this study, mannitol was used as organic carbon source to investigate its effects on the accumulation of biomass, polyunsaturated fatty acids and fucoxanthin of Phaeodactylum tricornutum under this mixtrophic condition. The concentration of mannitol at 2 g/L was finally selected for the cultivation. Furthermore, tea polyphenols at 0.2 g/L could effectively promote the utilization of mannitol. Compared with that of autotrophic culture, the final biomass was increased by 63%, and the yield of fucoxanthin reached to 75.3 mg/L, increased by 90%; EPA（Eicosapentaenoic acid） accounted for 36% of the total lipid, increased by 35%. This study provided a potential mixtrophic carbon source and antioxidant for improving production of EPA and fucoxanthin by P. tricornutum.

Key words: Phaeodactylum tricornutum, mannitol, tea polyphenols, EPA, fucoxanthin