Abstract: Magnetic Fe₃O₄ was synthesized by chemical coprecipitation method, and used as a raw material for preparing Fe₃O₄/MgAl-LDH. The calcined Fe₃O₄/Mg(Al)O was taken as the catalyst for the transesterification of microalgae oil with methanol, and the biodiesel yield was used to evaluate the activity of the catalyst. Several instruments including TG-DTG, XRD, SEM, EDS, TEM, N₂ absorption-desorption and VSM were employed to characterize the catalysts. The results show that MgAl-LDH and Mg(Al)O are successfully formed on Fe₃O₄ particles which have a strong magnetic response. When the reaction time is 4 h and the methanol/oil mol ratio is 13:1, the biodiesel oil yield reaches to 90%. After using for three times the catalyst still has certain activity and can be easily separated and recycled.