The influence of monoethanolamine (MEA) as a CO2 absorbent on photoautotrophic culture of CO2-fixing microalgae was investigated. When 300 ppm MEA (4.92 mM) was added to blank culture medium, the dissolved inorganic carbon and the molar absorption ratio increased to 51.0 mg/L and 0.34 mol(CO2)/mol(MEA), respectively, which was an almost 6-fold increase in CO2 solubility. When free MEA up to 300 mg/L was added to a green alga Scenedesmus sp. culture that was supplied 5% (v/v) CO2 at 0.1 vvm, both cell growth rate and final cell density were enhanced compared to when no MEA was added. The cell growth rate reached 288.6 mg/L/d, which was equivalent to 539.6 mg-CO2/L/d as a CO2-fixation rate and enhancement of about 63.0% compared to not adding MEA. Chlorophyll-a content and nitrate consumption rate increased correspondingly. MEA doses higher than 400 mg/L inhibited cell growth, probably due to toxicity of the carbamate intermediate. (C) 2012 Elsevier Ltd. All rights reserved.