Worldwide petroleum reserves are decreasing rapidly; therefore, looking for sustainable and renewable energy is currently one of the targets of scientists. Biodiesel which can satisfy these requirements is synthesized by the transesterification of plant/animal oil with alcohols, typically methanol, catalyzed by acid or base. Calcium oxide (CaO) derived from the eggshell shell can be used as a catalyst in the transesterification of oil with methanol because of its low solubility in methanol, high alkalinity and reusability which conform to environmentally-friendly process. In this research, induction period, rapid reaction period and equilibrium period were observed in the rate-time curve when CaO was used as a catalyst for the transesterification of soybean oil with methanol. CaO was preheated in methanol for 15 minutes before soybean oil was added and reaction started. It was found that pre-heating of CaO could significantly shorten the reaction time and resulted in 92.53% of the yield of fatty acid methyl esters. Moreover, this study contributes new information when CaO is used as the catalyst for biodiesel production