We assumed that the reaction process of in situ transesterification followed the following steps: (1) microalgae cells were destroyed or partially destroyed; (2) lipids within microalgae cells were released outside through cells wall; (3) the lipids contacted with reactants; (4) reaction took place. The solvent (n-hexane) added was of importance because the contact of algal lipids with reactant was the vital step in transesterification reaction and the addition of nhexane could help lipids within microalgae cells be easily extracted. As reported in our previous study [15], n-hexane was an optimal solvent because the biodiesel yield could be dramatically improved when n-hexane was added. Beside, nhexane is commonly used for oil extraction, and it has been demonstrated that more lipids could be easily extracted from microalgae cells by using n-hexane as an extraction solvent [1, 21, 22].