Esterification of oleic acid with ethanol catalyzed by organophosphonic acid-functionalized silica SG-T-P was optimized using response surface methodology (RSM). The interactive effect of catalyst to FFA weight ratio and molar ratio of alcohol to acid were more significant than that of reaction temperature. The optimum values for maximum conversion ratio obtained by a Box-Behnken center-united design reached 77.02 +/- 0.62% when the reaction was carried out at 112 degrees C for 10 h with a molar ratio of alcohol to oleic acid of 8.8:1 and a content of 14.5 wt.% triethylenetetramine bis(methylene phosphonic acid)- functionalized silica catalyst SG-T-P. The research results show that SG-T-P is a potential catalyst for biodiesel production that can adsorb water from the reaction mixture at the same time. (C) 2012 Elsevier Ltd. All rights reserved.