Microalgae fix CO2 as energy source and afford biomass and high valued products such as carotenoids, pigments, proteins, and vitamins that can be used for the production of nutraceuticals, pharmaceuticals, animal feed additives, cosmetics, etc. Carbon dioxide is the sole source of carbon and it is supplied continuously for the microalgal cultivation. But undissolved CO2 is lost by outgassing and sufficient dissolved CO2 should be provided to avoid carbon limitation. The effect of CO2 mass transfer with different CO2 concentrations, aeration rate of gas, bubble size, baffle type and baffle number on the growth of Chlorella sp. AG10002 was investigated and the optimized conditions for the enhancement of biomass productivity were determined. We confirm that these results can be provided as basic data to improve the CO2 mass transfer ability for the high density culture of Chlorella sp. and some microalgae having commercial value.