Nanometer magnetic solid base catalysts were prepared by loading CaO on Fe(3)O(4) with Na(2)CO(3) and NaOH as precipitator, respectively. The optimum conditions for preparation of this catalyst were investigated. The influence of the proportion of Ca(2+) to Fe(3)O(4) on the catalytic performance has been studied. The catalyst with highest catalytic activity has been obtained when the proportion of Ca(2+) to Fe(3)O(4) is 7:1: the catalytic activity of the catalyst calcined from Ca(OH)(2) to Fe(3)O(4) is better than that calcined from CaCO(3) to Fe(3)O(4); under the conditions of methanol/oil molar ratio of 15:1, catalyst dosage of 2 wt% and temperature of 70 degrees C, the biodiesel yield reaches to 95% in 80 min, even to 99% finally. The catalytic activity and recovery rate of the nanometer magnetic solid base catalysts are much better than those of CaO. Calcination temperature was determined by differential thermogravimetric analysis. Ca(2)Fe(2)O(5), a kind of new metal multiple oxide, was found in the catalyst through X-ray diffraction. At the end, these catalysts were characterized by scanning electronic microscope (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). (C) 2009 Elsevier Ltd. All rights reserved.