Calcium oxide (CaO) catalysts derived from waste shells of egg, oyster and clam were prepared and used in the methanolysis of soybean oil. Eggshells were subjected to ultrasound irradiation and mollusc shells were subjected to calcination-hydration-calcination cycles to increase the surface area of CaO and improve its catalytic activity. The catalysts were characterized by XRD, TPD-CO2, TG-DSC, DLS and N-2 adsorption, while the catalytic activity for the methanolysis of soybean oil was evaluated. Five hours of sonication reduced the CaO particle size by 34%, which resulted in a 56% increase in the activity. Two cycles of hydration-dehydration applied to the material obtained by calcination of oyster shells provided CaO with 27 m(2) g(-1). The transesterification rate was 2.5 times higher than that obtained with the untreated sample. After treatments, highly active CaO was obtained which indicates its enormous potential for biodiesel production. A kinetic model assuming the adsorption of methoxide anions on the surface of CaO particles was proposed.