The use of a heterogeneous catalyst, in the transesterification reaction of refined and acidic cottonseed oil for the production of methyl-esters (biodiesel) has been studied. The basic Mg-Al-CO(3) hydrotalcite catalyst used showed a high activity for methanolysis and esterification reactions in a refined and an acidic cottonseed oil as well as in a representative high water content animal fat feed. The experiments were performed in a temperature range between 180 and 210 degrees C in a batch reactor. The methanol to vegetable oil molar ratio was 6 to 1, while the catalyst concentration was fixed at 1 wt.% of the oil mass. Non-calcined and calcined forms of the catalyst were tested. The activity of the calcined catalyst was lower than the initial activity of the non-calcined catalytic system but it appeared the same with the reused non-calcined system. (C) 2007 Elsevier Ltd. All rights reserved.