The esterification of free fatty acids (FFA) can be used to produce biodiesel from high FFA oils. In this work, a new eco-friendly catalyst for the esterification of oleic acid with methanol has been prepared from a waste material, Amazon flint kaolin, that was thermally treated (at 850 and 950 degrees C) and activated with sulfuric acid solutions (1 M and 4 M). The activated metakaolin samples were characterized by X-ray diffraction, scanning electron microscopy, N-2 adsorption-desorption and adsorption studies of pyridine using TG/DTG and FTIR analysis. The leached metakaolin treated at 950 degrees C and activated with 4 M sulfuric acid solution showed the highest surface area (406 m(2)/g), the highest number of acid sites (237.7 mu mol/g) and offered the maximum esterification activity (98.9%) at 160 degrees C, an acid:methanol molar ratio of 1:60 and 4h reaction time. The influences of reaction parameters such as the molar ratio of the reactants, alcohol chain length, temperature and time have also been investigated. Based on the catalytic results, Amazon flint kaolin is found to be a promising raw material for the production of new solid acid catalysts for the esterification of FFAs. (c) 2010 Elsevier B.V. All rights reserved.