During Rhizopus oryzae-mediated methanolysis of triglycerides for biodiesel production, the amount of 1,2-DG and 2-MG as well as the ratio of 1,2-DG/1,3-DG and 2-MG/1-MG differed significantly in different reaction medium, which indicated that solvent might be a crucial factor that would influence the acyl migration rate, leading to varied biodiesel yield. In this paper, the influence of solvent and their properties on acyl migration kinetics of both 1,2-diglyceride and 2-monoglyceride were investigated systematically. It was found that decreasing solvent polarity would give increasing acyl migration rate constants in general. Solvent polarity influenced the acyl migration rate through the influence of the charge dispersion of the transition state. High polarity of the solvent was unfavorable to the transition state charge dispersion, which would increase its energy state, and thus decreased the acyl migration rate and then led to relatively lower methyl ester yield. (C) 2010 Elsevier Ltd. All rights reserved.