Biodiesel synthesis from acid oil (AO) containing high free fatty acids (FFA) over pore expanded sulfonic acid functionalized mesostructured SBA-15 was studied. Reaction parameters affecting the FAME yield were optimized using Taguchi design. 99% FFA conversion was obtained under optimum conditions viz. at 100 degrees C with 4 wt.% catalyst amount and 1:15 oil to methanol ratio after 8 h. Kinetic study revealed that the reaction followed pseudo first order kinetic law. (C) 2014 Elsevier B.V. All rights reserved.