Abstract: Phaeodactylum tricornutum was cultured in medium with different urea concentration to investigate its growth and fatty aeid composition. The results showed that adding of urea in medium could improve the cell intensity of P. tricornutum markedly. The growth increased with urea concentration rising from 0 to 8.0 mmol/L. The content of eicosapentaenoic acid （EPA） and polyunsaturated fatty acids （PUFAs） increased at first and then dropped with a maximum EPA content （19.1%） at 2.1 mmol/L of urea. The cell intensity was relatively high when 2.1 mmol/L was set as the optimal urea concentration. Considering biomass of algae and production of EPA and PUFAs, this urea concentration is also suitable to get higher production of both.