Biodiesel produced by vegetable oil transesterification is a potential alternative fuel to diesel regarding the limited resources of fossil fuel and its environmental concerns. In this paper, N-methylimidazole functionalized anion exchange resin (R+-OH-) containing NaOH was synthesized through two-step method and applied for transesterification of soybean oil. R+-OH- was found to show some polarity due to the functional groups of N-methylimidazole and hydroxyl, and NaOH could be absorbed in R+-OH- to form R+-OH- (Na). Both soybean oil and methanol will be compatible to the partly-polar R+-OH- (Na), and the reaction will be enhanced by the co-catalysis of R+-OH- with NaOH. The properties of R+-OH- (Na) were studied, such as ion exchange capacity, stability and microstructure. The influences of the molar ratio of methanol to soybean oil, stirring speed and the amount of R+-OH- (Na) were investigated. The conversion of soybean oil was up to 97.25% at the optimal condition: molar ratio of methanol to soybean oil 12:1, the amount of catalyst 2.5%, reaction temperature 50 degrees C. stirring speed 570 rpm and reaction time 10 h. The co-catalysis of R+-OH- with NaOH improved the yield of biodiesel greatly, and R+-OH- (Na) could be reused after regeneration. (C) 2011 Elsevier B.V. All rights reserved.