1The Mg-Fe layered double hydroxides (Mg-Fe LDH) precursors were prepared using 2 improved urea method and characterized by XRD, ICP-AES and SEM analyses, indicating 3 that the pH played a crucial role in the precipitation. The precipitation of the Mg-Fe LDH 4 precursors was obtained when adjusting the initial pH to 9.3 by adding NaOH solution and 5 controlling urea/Fe 3+ molar ratio of 36 in the precipitation solution at 110°C for 10 h, where 6 the relative yield was 85.4%. The calcined Mg-Fe LDH (LDO) were determined by XRD and 7 CO 2 -TPD analyses. The LDO with Mg/Fe molar ratio of 3 (LDO-3) was found to have the 8 highest catalytic activity for the transesterification of microalgae oil due to the strongest 9 basicity and highest crystallinity. Finally, the stability and the leaching of the catalytically 10 active species as well as the reusability of the LDO-3 were confirmed by hot-filtration test 11 and multiple reuses. The LDO-3 catalyst could be reused, but catalytic activity decreased 12 after each run due to active species leaching although it remained high activity for the fourth 13 uses. 14 Keywords 15 Mg-Fe layered double hydroxides; Mg-Fe mixed oxides; improved urea method; base catalyst; 16 biodiesel 17 18