Three Sn(IV) complexes, named butyl stannoic acid (BTA), di-n-butyl-oxo-stannane (DBTO) and dibutyltin dilaurate (DBTDL), were initially tested as catalysts for esterification reaction of fatty acids in the presence of methanol as alcoholysis agent. Parameters like reaction time, temperature, and catalyst amount were systematically evaluated in this work. All complexes were active at relative high reaction temperatures, but BTA displayed the highest activity. Former studies have already demonstrated that these same complexes display good catalytic activity in methanolysis of triacylglycerides (TAGs). These results prompted us to test BTA catalyst also in simultaneous esterification/transesterification reactions from a mixture of free fatty acids (FFAs) and TAGs in the presence of methanol. BTA was able to convert the mixtures in to fatty acid methyl esters (FAMEs) with good yields, with simple isolation processes. The results obtained and discussed in this work can help the development of new catalytic systems to biodiesel production from oils with very high acid content. (C) 2012 Elsevier B.V. All rights reserved.