Studies were carried out to evaluate the potentiality of diether used in transesterification and investigate the effects of diether type, catalyst concentration, molar ratio of methanol/oil, and temperature on biodiesel production. Experiment results showed that four selected diethers, including 1,2-dimethoxyethane, 2,2dimethoxypropane, diethoxymethane, and 1, 1 -diethoxyethane, converted a methanol/oil two-phase system into a diether/methanolloil one-phase system when they were added up to a critical volume. There were no significant differences among these four diethers in forming one-phase system with sunflower oil. The conversion rates using diethers as cosolvents were slightly higher than those using monoethers under the same reaction condition. The optimal catalyst (KOH) concentration of 6.90 g/L and methanol/oil molar ratio of 9:1 were determined when diethoxymethane was used to intensify the transesterification. The higher the reaction temperature (from 25-65 degrees C) was, the quicker the transesterification was. It took 7 min to get a 97.0% methyl ester concentration at 25 degrees C and only 2 min to reach 96.7% at 65 degrees C.