Mg-Zn mixed oxides with different Mg to Zn mole ratio were synthesized using a CO2 precipitation method and studied for the transesterification of soybean oil with methanol to produce fatty acid methyl esters (FAME) or biodiesel. The Mg to Zn optimized mole ratio was found to be about 3, denoted as Mg3Zn1. Different Mg3Zn1 catalysts synthesized using co-precipitation (Cop), impregnation (IMP) and urea hydrolysis (urea) methods were also studied for FAME production. All Mg-Zn mixed oxides were characterized by FOR, XRD, TG/DTA, CO2-TPD and HR-TEM/SEM-EDX techniques. Formation of FAME in this study was influenced by the Mg to Zn molar ratio and preparative parameters. The maximum FAME content (90% mass) was obtained at 65 degrees C for the Mg3Zn1 CO2 precipitation (Mg3Zn1 CO(2)ppt) catalyst wherein a mixed oxide lattice Zn-Mg-O was established by HR-TEM. The contribution towards the greater biodiesel content was mainly attributed to the Zn-Mg-O lattice basic sites. The catalytic activity of Mg-Zn mixed oxides for FAME formation increases as follows; ZnO approximate to Mg3Zn1 urea < Mg1Zn1 approximate to Mg3Zn1 IMP < Mg5Zn1 < MgO < Mg3Zn1 Cop < Mg3Zn1 CO(2)ppt. (C) 2014 Elsevier B.V. All rights reserved.