A series of supported CaO catalysts with NaY, KL and NaZSM-5 zeolites as supports were prepared by microwave irradiation and used to catalyze the transesterification of methanol with soybean oil. The activities of synthesized catalysts were investigated compared to pure CaO. It was found that the activity of CaO catalyst increased after supported on zeolites, and the CaO/NaY exhibited the best performance. The improved catalytic activity was attributed to the increase of BET values and the concomitant increase of basic strength and basicity after dispersed on NaY zeolite through microwave irradiation. The prepared catalysts were characterized by several techniques such as X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area, scanning electron microscopy (SEM) and the Hammett indicator method. In addition, the factors affecting biodiesel yield were investigated to optimize the reaction conditions. A biodiesel yield of 95% was achieved (using the CaO/NaY catalyst) with 30 wt.% of CaO loading on NaY zeolite, methanol/soybean oil molar ratio 9, reaction temperature 65 degrees C, reaction time 3.0 h and catalyst/oil mass ratio 3%. The results indicated that the supported catalyst had the capacity of water resistance and acid resistance. A high yield (more than 80%) could be obtained when the acid value and the water content of oil were less than 4 mg KOH/g and 1.5%, respectively. (c) 2012 Elsevier B.V. All rights reserved.