This study introduces a two consecutive steps basic-acid transesterification process, (denominated Transesterification Double Step Process - TDSP) for biodiesel production from vegetable oils. The process involves homogeneous consecutive basic-acid catalysis steps and is characterized by formation of well-defined phases, easy separation procedures, high reaction velocity and high conversion efficiency. The proposed TDSP is different in relation to other traditional two-step procedures which normally include acid esterification followed by basic transesterification. or enzymatic or even supercritical transesterification conditions. The biodiesel (fatty acid methyl esters) was analyzed by standard biodiesel techniques in addition to H-1-NMR, indicating high quality and purity biodiesel products. The transesterification of sunflower and linseed oils resulted in oil conversions higher than 97% corresponding to yields of 85%. A probable reaction mechanism responsible for the process is presented. (C) 2009 Elsevier B.V. All rights reserved