This means that the alkaline earth metal might have positive effect on the sulfonic acid functional groups on the SiO2 shell. Moreover, the recycling test also displays that SrFe2O4/SiO2-SO3H had better stability in catalyzing esterification (Fig. 3). Besides, the XRD profile indicates that the main structure of SrFe2O4 is Sr7Fe10O22 (Fig. 1), and the surface area by BET analysis of SrFe2O4 was 2.3m2/g cat.To reveal the best operating conditions for esterification and transesterification, a series of experiments were performed. The three-dimensional diagrams given in Figure 4 indicate the effects of the reaction time and temperature on conversions of mixed oil to biodiesel by acid catalysts and soybean oil to biodiesel by NaOH