The purposes of this study were to find the optimum level of supplementing CO2 for increasing the bio-mass and hydrocarbon production of B. braunii KMITL 2 (A race) and to determine the effects of CO2 level on CO2 fixation and biodiesel properties. The experimental results showed that the alga supplemented with 10% CO2 produced the highest biomass (1.48 +/- 0.02 g L-1) and CO2 fixation rate (100.43 +/- 1.42 mg L-1 d(-1)) that were 2.7 and 5.3 times higher than the control (0.04% CO2). The gravimetric hydrocarbon content (36.82 +/- 3.39%) and hydrocarbon titer (0.35 +/- 0.03 g L-1) of the alga supplemented with 5% CO2 were 1.6 and 2.7 times higher than the control. Cultivation of this strain under 5% CO2 gave the highest hydrocarbon yield and good biodiesel properties with the lowest iodine value and a higher CN value than the ASTM D6751 and EN 14214 fuel standards. (C) 2017 Elsevier Ltd. All rights reserved.