A natural porous silica, pumice, was studied as heterogeneous catalyst in the transesterification reaction of sunflower oil and frying oil with methanol for biodiesel production. This low cost natural porous material was subjected to ion exchange with a KOH aqueous solution in order to increase its activity. The dependence of the reaction variables such as temperature, reaction time, catalyst loading and methanol/oil molar ratio were studied using sunflower oil and waste oil as feedstock. Moreover, in order to save production costs, the reusability of the catalyst in the transesterification reaction was studied. (C) 2010 Elsevier B.V. All rights reserved.