Abstract: Growth and interspecies competition were studied between harmful algal bloom species Chattonella marina and three typical diatoms (Chaetoceros curvisetus, Phaeodactylum tricornutum, and Skeletonema costatum) under different nutrient conditions and initial cell densities using batch cultures.Results showed that the maximum cell densities of C.marina were not affected by the initial cell density in enriched f/2 cultures.However, the maximum cell density was significantly reduced in nutrient limitation, which was only 15.4% of that in f/2 cultures.The growth of C.marina was significantly inhibited in co-cultures with diatoms, which resulted 100% death of C.marina after 10-16 days in co-cultures under f/2 medium.On the contrary, the growth of C.curvisetus and P.tricornutum were not significantly influenced in co-cultures of C.marina under f/2 medium.While the growth of S.costatum was significantly inhibited in co-cultures, the maximum cell density was less than 50% of those in mono-cultures.However, the growth of C.marina and all of the three diatom species were significantly inhibited in co-cultures under nutrient restriction.Results of this study suggested that these small diatoms might have competitive advantages over C. marina under nutrient enriched conditions, however, rapid decline in nutrient concentration caused by the outbreak of diatom blooms might be beneficial to the growth of non-diatoms.