A series of CaO solids have been prepared by means of thermal treatment of the following precursors: carbonate, acetate, oxalate, nitrate, and two hydroxides obtained previously by precipitation of calcium acetate and nitrate in basic medium. These solids show distinct reaction rates in the catalytic transesterification of triglycerides with methanol to obtain biodiesel. An exhaustive characterization study using X-ray diffraction, N(2) adsorption-desorption isotherms, infrared spectroscopy of pyrrole adsorbed, and temperature-programmed desorption of CO(2) allowed us to determine the influence of the physicochemical properties (crystallite size, surface area and porosity) and surface basicity (amount and distribution of basic sites with different strength) on the overall catalytic activity. We have found that CaO obtained by decomposition of calcium carbonate, which shows the highest amount and surface density of very strong base sites, catalyzes triglycerides transesterification with higher rates. (C) 2010 Elsevier B.V. All rights reserved.