Abstract: Although most microalgae are photoautotrophs, some microalgae can use organic carbon substances as the sources ofenergy and carbon for cell growth? Mixotrophic growth provides an alternative way for high-density cultivation of microalgae?Phaeodactylum tricornutum has been regarded as a typical diatom in many studies, but it does not possess the heavily silicifiedcell wall characteristic of many bacillariophyta? This makes P? tricornum an organism particularly useful for the physiologicalstudy of diatoms? Moreover, P? tricornum has been studied intensively as a potential source of polyunsaturated fatty acids(PU-FAs), mainly Eicosapenyaenoic acid(EPA)? Cultivation is performed mainly under photoautotrophic conditions, and this mode ofgrowth results in a relatively low growth rate and biomass concentration? In order to determine the ability of mixotrophic growthand enhance the biomass concentration, effects of organic carbon sources and nitrogen sources on the growth of P? tricornumwere investigated? The experimental method included the following four parts: First, eight kinds of organic carbon sources wereadded to the culturemedium at the concentrations of 5mmol/L and 50mmol/L, such as glucose, fructose, galactose, sodium ac-etate, sodium citrate, sodium lactate, glycerol, and ethanol? Second, nine different concentration levels of glycerol were set,namely 5, 10, 50, 100, 200, 400, 600, 800mmol/L, and 1000mmol/L This study also included nine different concentrationlevels of glucose, namely 50, 100, 150, 200, 300, 400, 500, 750mmol/L, and 1000mmol/L? And seven different concentra-tion levels of glucose were also set, namely 10, 50, 100, 150, 200, 300mmol/L, and 400mmol/L? Third, under themixotrophic growth with 50mmol/L glycerol, four kinds of nitrogen sources were added to the culture medium at the concentra-tions of 0.22mmol/L and 2.2mmol/L, such as sodium nitrate, ammonium chloride, ammonium nitrate, and urea? Fourth, di-fferent concentration levels of urea were set, namely 0.088, 0.176, 0.22, 0.44, 0.88, 2.2, 4.4, 8.8mmol/L, and 88mmol/L? The results showed that P? tricornutum could grow mixotrophically? When the concentrations of organic carbon sources were5mmol/L and 50mmol/L, glucose, fructose, sodium acetate and glycerol could promotethegrowth of P? tricornutum efficiently,but sodium lactate and ethanol inhibited its growth? Galactose and sodium citrate varied with the concentrations of organic carbon? The optimum concentration ranges of glycerol, glucose and sodium acetate were 5 800mmol/L, 100 400mmol/L and 50300mmol/L, respectively? In the mediumwith 50mmol/L glycerol, 400mmol/L glucose or 150mmol/L sodium acetate, respective-ly, after 14d culture, the maximum biomass were 1.45-fold, 1.25-fold, 1.11-fold of that obtained under photoautotrophic cond-ition Under mixotrophic growth with glycerol, when the concentration of nitrogen sources was 2.2mmol/L, there were not signif-icant differences among four kinds of nitrogen sources? When the concentration of nitrogen sources was 0.22mmol/L, the optimumnitrogen sourcewas urea, followed by ammonium nitrate? The optimal concentration range of urea was 0.88±8.8mmol/L, buttherewere not significant differences among these treatments? When the concentration of urea was 4.4mmol/L, the maximumbiomass was 131g/L?