SO2 is very rapidly hydrated to sulfurous acid in water solution at pH value above 6.0, wherebysulfi te is yielded from the disassociation of protons. We aimed to improve the sulfi te transformation effi ciency and provide a basis for the direct utilization of SO 2 from fl ue gas by a microalgal suspension. Chlorella sp. XQ-20044 was cultured in a medium with 20 mmol/L sodium sulfi te under different physicochemical conditions. Under light conditions, sulfi te concentration in the algal suspension reduced linearly over time, and was completely converted into sulfate within 8 h. The highest sulfi te transformation rate (3.25 mmol/(L？h)) was obtained under the following conditions: 35°C, light intensity of 300 μmol/(m 2 ？s), NaHCO 3 concentration of 6 g/L, initial cell density (OD 540 ) of 0.8 and pH of 9–10. There was a positive correlation between sulfi te transformation rate and the growth of Chlorella , with the conditions favorable to algal growth giving better sulfi te transformation. Although oxygen in the air plays a role in the transformation of SO 3 2ˉ to SO 4 2ˉ, the transformation is mainly dependent on the metabolic activity of algal cells. Chlorella sp. XQ-20044 is capable of tolerating high sulfi te concentration, and can utilize sulfi te as the sole sulfur source for maintaining healthy growth. We found that sulfi te ≤20 mmol/L had no obvious effect on the total lipid content and fatty acid profi les of the algae. Thus, the results suggest it is feasible to use fl ue gas for the mass production of feedstock for biodiesel using Chlorella sp. XQ-20044, without preliminary removal of SO 2 , assuming there is adequate control of the pH.