The catalytic activity of the walnut shell ash was investigated in the biodiesel production by the sunflower oil methanolysis. The catalyst was characterized by the TG-DTA, XRD, Hg porosimetry, Ny physisorption, SEM, and Hammett method. In addition, the effects of the catalyst loading and the methanolto-oil molar ratio on the methyl esters synthesis were tested at the reaction temperature of 60 degrees C. The walnut shell ash provided a very fast reaction and a high FAME content (over 98%). As the reaction occurred in the absence of triacylglycerols mass transfer limitation, the pseudo-first-order model was employed for describing the kinetics of the reaction. The catalyst was successfully reused four times after the regeneration of the catalytic activity by recalcination at 800 degrees C. (C) 2019 Elsevier Ltd. All rights reserved.