Abstract: Microalgae are potential sources of polyunsaturated fatty acids (PUFAs), mainly EPA (Eicosapentaenoic acid) and DHA (Docosahexaenoic acid). However, the EPA productivity of microalgae is lower compared with bacteria and fun-gi, and the reason is mainly the low growth rate and biomass under photoautotrophic conditions. To promote the EPA pro-ductivity, culture conditions such as culture temperature, irradiance, pH, nutrition sources and concentrations have been investigated. Nevertheless, some microalgae grow rapidly and have a higher biomass under mixotrophic conditions than which under photoautotrophic conditions. Pinguiococcus pyrenoidosus belongs to Pinguiophyceae, Pinguiococcus genara. The percentage of rude lipid content of the microalgae is 27.45%, among which EPA and saturated fatty acids (14:0, 16:0) are high, but the contents of other kinds of fatty acids are very low. So Pinguiococcus pyrenoidosus is a good materi-al for producing PUFAs and saturated fatty acids. So far, there is little information about the mixotrophic growth on the growth rate and fatty acid composition of the microalgae. In order to determine the optimal culture conditions, EPA pro-ductivity and saturated fatty acids productivity, effects of different carbon resources (inorganic carbon compounds and or-ganic carbon compounds) on the growth and fatty acid composition in P. pyrenoidosus CCMP 2078 were investigated. The experimental method included the following three parts: First, three different concentration levels of CO2 were set, namely 0.5%, 1.0% and 1.5%; Second, four different concentration levels of NaHCO3 were set, namely 5, 10, 20 and 25retool/L; Third, four different concentration levels of glucose were set, namely 5, 10, 20 and 40g/L, respectively. Pa-rameters of cell density and fatty acid composition were measured. The results showed that (1) Growth of P. pyrenoidosus CCMP 2078 was promoted by adding proper concentrations of carbon sources. The optimal concentrations of carbon sources for growth were 0.5% CO2, 5mmol/L NaHCO3 and 20g/L glucose, and the cell density of late logarithmic phage were 3.10-fold, 1.47-fold and 2.78-fold of that obtained under control; (2) When added the carbon sources except the low concentration of glucose, the percentages of TPUFA (Total polyunsaturated fatty acids)and EPA, and cell EPA and TSFA (Total saturated fatty acids) content were all lowered, but the percentage of TSFA was increased; (3) The yield of SFAs (Saturated fatty acids)and EPA were enhanced when added low concentrations of carbon sources. The yield of EPA and TSFA were 2.30-fold and 2.69-fold when added 0.5% CO2 of those obtained under control, respectively. The yield of TSFA was 1.85-fold when added 5mmol/L NaHCO3 of that obtained under control. The maximum yield of EPA and TSFA were 2.11-fold and 1.58-fold when added 5g/L and 10g/L glucose of those obtained under control, respectively. Therefore, low concentration of CO2 was the optimal culture condition for the growth of P. pyrenoidosus CCMP 2078, and also for the yield of EPA and SFAs. The increases of EPA and TSFA were resulted by the enhancement of the biomass concentration.