Biodiesel is produced by transesterification reaction of oils catalyzed by homogeneous catalysts, with the latter being non-recoverable and promoter of solubility of the produced glycerol into the otherwise immiscible ester phase, which have to be purified. The need for purification of products is eliminated if heterogeneous catalysts are employed, with the added advantage of the catalyst recovery, however, with disadvantage of requiring drastic reaction conditions (elevated temperatures and pressures, longer reaction times) significantly increasing the costs of production. To overcome such problems, several catalysts were developed, with the sulfonated ones being the most prospective for industrial applications. Thus, the objective herein was to develop a sulfonated heterogeneous catalyst using activated carbon produced from corncobs as precursor material and employ it in microwave-assisted transesterification reactions of soybean oil with ethanol. The optimum operational conditions employed for the reaction were microwave variable power of 0-600 W, catalyst-to-oil mass ratio of 20%, alcohol-to-oil molar ratio of 6:1 and reaction time of 20 min. The catalyst successfully catalyzed the transesterification reaction in times as short as 20 min, resulting in a pure biodiesel phase with yield of 88.7%. The catalyst was reused in five subsequent reaction cycles without loss of its catalytic activity. (C) 2019 Elsevier Ltd. All rights reserved.