Abstract: As a new kind of solvent, deep eutectic solvent can be used as catalyst to reduce the production cost of biodiesel, simplify the purification process and reduce environmental pollution. In this study, an acidic deep eutectic solvent (DES) composed of ChCl and PTSA has been studied as the catalyst in transesterification of sunflower oil and methanol to produce biodiesel. The optimal conditions were obtained by single factor experiment: reaction temperature was 120 ℃, reaction time was 50 min, the amount of DES-5 was 5%, the molar ratio of alcohol to oil was 8∶1, and the rotation speed was 600 r/min. In this condition, the esterification conversion reached 98.23%±0.06%. The characteristics of methyl esters of sunflower oil catalyzed by DES-5 and p-toluenesulfonic acid (PTSA) were also studied. It was found that the hydroxyl value, water content and glyceryl ester were lower when the methyl esters were obtained using DES-5 as catalyst. The results show that DES can be used in the preparation of biodiesel and high purity biodiesel products can be obtained.