To increase the lipid productivity and thus to reduce the production cost of microalgal biodiesel, effects of cultivation conditions including KNO(3)-level, CO(2) concentration and irradiance on the cell growth, chlorophyll a content and lipid accumulation of Chlorella vulgaris were systematically investigated in a membrane sparged photobioreactor. The biochemical compositions including carbohydrates, proteins and lipids were analyzed simultaneously by the FT-IR spectroscopy. The results showed that the largest biomass productivity and the highest lipid content were obtained at different cultivation conditions. The algae should be harvested at a point that optimized the biomass productivity and lipid content. When the cultivation conditions were controlled at 1.0 mM KNO(3), 1.0% CO(2) and 601 mu mol photons m(-2) s(-1) at 25 degrees C, the highest lipid productivity obtained was 40 mg L(-1) d(-1), which was about 2.5-fold that had been reported by Illman et al. (2000). The influences of cultivation conditions on the cell growth, lipid accumulation, and other biochemical compositions of cells were further discussed and illustrated by a schematic which was also useful for other microalgal species. (C) 2010 Elsevier Ltd. All rights reserved.