To investigate the effects of different C/N ratios on the growth and cell biochemical components of Chlorococcum sp. Chlorococcum sp. was cultured with C/N ratios of 0:1, 3:1, 6:1, 9:1, 12:1 and 15:1 for 7 days, and the initial inoculation density was 300×10⁴ cells/mL. The results showed that mixotrophic cultivation could significantly increase cell density, specific growth rate and biomass (P<0.05). While the ratio of C/N was 9:1, the biomass reached the maximum value of 0.36 g/L. Under mixotrophic cultivation, the protein and total lipid mass fraction of Chlorococcum sp. decreased with the increasing of C/N. When C/N was 12:1 and 15:1, the protein and total lipid mass fraction reached the minimum values of 33.76% and 6.67%, respectively. Carbohydrate mass fraction increased firstly and then decreased with the increasing of C/N. Furthermore, the maximum value (30.57%) was obtained by 9:1 group which was significantly higher than other groups (P<0.05). The mass fraction of saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA) increased with the increasing of C/N ratios with the maximum values in 15:1 group. By contrast, increasing of C/N ratios had an adverse effect on polyunsaturated fatty acid (PUFA) content of Chlorococcum sp. with the minimum value (64.67%) in 15:1 group. It is concluded that the moderate up-regulation of C/N ratios could increase the biomass and promote the synthesis of SFA and MUFA of Chlorococcum sp., but not for PUFA.