A new reaction system for biodiesel production by the base-catalyzed transesterification process has been developed. Bentonite is used as a water adsorbent in the traditional homogeneous base-catalyzed transesterification reaction system to create a heterogeneous system that improves the reaction efficiency. The influence of bentonite on the NaOH-catalyzed methanolysis of soybean oil and the accompanying reaction mechanisms were investigated. It was found that an appropriate introduction of bentonite can promote the methanolysis. By the rapidly removal of the water from the system, bentonite enhances the transformation of NaOH to the catalytically active methoxide species. Further, the main side reactions are significantly inhibited. The methanolysis of triglycerides took place in the liquid phase rather than in the solid phase. The introduction of bentonite also lowered the soap concentration in crude biodiesel, which was beneficial for the post-treatment to generate refined biodiesel. (C) 2016 Elsevier B.V. All rights reserved.