Transesterification of soybean oil and ethanol catalyzed by calcium oxides prepared from the calcinations of CaO,Ca(OH)2, limestone, and Ca(OH)2/CaO as solid base catalysts was investigated. It was found that the catalytic activitiessignificantly depended upon their base site strengths and their structures. Increases in catalytic performance of CaO could beachieved by loading Ca(OH)2 on CaO and calcinations at a high temperature. The catalytic reaction using a 9:1 molar ratio ofethanol to oil at 70 °C, using CaO loaded with 3.7 wt% Ca(OH)2 exhibited the optimal results, where the conversion of soybeanoil reached 96.3% after 10 hrs of the reaction.