Abstract: The article is to explore the effects of inorganic nitrogen with various concentrations to the growth and cyst of Scrippsiella trochoidea.The study indicates NO₃-N is favorable to cell growth, while NH₄-N is preferable to absorb the vegetative cells.The antioxidant enzyme activities decreased along with rising concentration of nitrogen.But the different nitrogen source had different effects when the concentration and growth period were different.For example, compared with NO₃-N, 90 μM NH₄-N could promote the antioxidant enzyme activities in the phases of exponential growth, and 10 μM NH₄-N could promote the antioxidant enzyme activities in the phases of plateau.For other periods, these two nitrogen sources have less influence, which could be attributed to the prior absorption of NH₄-N.