In this study, a direct transesterification process using 75% ethanol and co-solvent was studied to reduce the energy consumption of lipid extraction process and improve the conversion yield of the microalgae biodiesel. The addition of a certain amount of co-solvent (n-hexane is most preferable) was required for the direct transesterification of microalgae biomass. With the optimal reaction condition of n-hexane to 75% ethanol volume ratio 1: 2, mixed solvent dosage 6.0 mL, reaction temperature 90 degrees C, reaction time 2.0 h and catalyst volume 0.6 mL, the direct transesterification process of microalgal biomass resulted in a high conversion yield up to 90.02 +/- 0.55 wt.%. (C) 2015 Elsevier Ltd. All rights reserved.