Three novel alkaline guanidine ionic liquids as amphiphilic catalysts have been successfully synthesized for two-phase transesterification, which can efficiently improve the catalytic activity for the synthesis of biodiesel. They were characterized by a series of techniques including H-1 NMR, thermal stability, electronegativity (DFT calculation), basicity and conductivity. It was demonstrated that 1,1,3,3-trimethyl-2-octyl-guanidine hydroxide(IL3) exhibited better catalytic activity compared with other base guanidine ionic liquid catalysts, which was related to the better basicity and electronegativity of the ILs. The experimental results indicated that catalytic performance was relative to both enough alkaline center and conductivity of ionic liquid catalysts, but the former was a main factor in the catalytic system. The catalytic performance also revealed that optimum catalyst dosage was about 6 wt.%, the appropriate reaction temperature was about 55 degrees C, the optimum n(Methanol)/n(Soybean Oil) for the biodiesel synthesis was about 15:1 and the suitable reaction time was 4 h on the basis of biodiesel yield of 97%. In addition, the reaction mechanism of the amphiphilic catalyst was illuminated by the interaction between the methoxyl group and the carbonyl group of the triglyceride after activating for two-phase transesterification. (C) 2015 Elsevier Ltd. All rights reserved.