Abstract: A novel solid base catalyst, CaO/MgO/Fe₃O₄ with magnetism used for production of clean biodiesel, was prepared and characterized by X-ray diffraction, transmission electron microscope, infrared spectrum and magnetism analysis. The catalytic activities of the fresh and the reused catalysts for the transesterification of peanut oil with methanol to produce biodiesel were investigated. The magnetic support of MgO/Fe₃O₄ with MgO loading of 5% was obtained by the magnetic matrix Fe₃O₄ dipped in Mg(Ac)₂ aqueous solution and then calcined at 600℃ in N₂. And CaO/MgO/Fe₃O₄ with CaO loading of 10% was prepared by MgO/Fe₃O₄ impregnated in Ca(Ac)₂ aqueous solution and further calcined at 700℃ in N₂. The particle of CaO/MgO/Fe₃O₄ was shell-core structure with the core mean diameter of 35nm. The results show that CaO/MgO/Fe₃O₄ has higher catalytic activity for transesterification reaction and could be separated easily from the reaction products in magnetic field. Both the conversion of peanut oil and recovery of the catalyst are above 90% under the conditions of atmospheric pressure, 65℃ for 2h, methanol/oil mol ratio of 12, and catalyst dosage (catalyst/oil) of 10%. The falling off of CaO from CaO/MgO/Fe₃O₄ during stirring reaction process was speculated as one of the reasons for the lower activity of the reused catalyst.