Abstract: Suitable conditions for biodiesel synthesis by the transesterification of lipid were studied by using microalgal oil extracted from Chlorella USTB-01 cells as feedstock and bronsted acid ionic liquid([C₄MIm]HSO₄) as a catalyst.Gas chromatograph-mass spectrometry(GC-MS) was used to determine fatty acids in the microalgal oil and its derived biodiesel.The results indicate that breaking the algae cell wall by grinding can significantly improve the extraction yield of algal lipid using Soxhlet extraction method;among the solvents tested,petroleum ether is the best solvent for the extraction.The major components of Chlorella USTB-01 oil are fatty acids containing C16 and C18.The optimum conditions for synthesizing the microalgae biodiesel are as follows:the molar ratio of methanol to the microalgae oil is 9:1,the dosage of the catalyst accounts for 8% of the mass of the microalgae oil,the reaction temperature is 150℃ and the reaction time is 6 h.Under this condition,the yield of biodiesel can reach 64%.GC-MS analysis shows that biodiesel from Chlorella USTB-01 oil is mainly composed of methyl esters of saturated fatty acid(C16:0) and unsaturated fatty acid(C18:2).The product is feasible to supplement fossil diesel fuel.