Transesterification of refined and crude vegetable oils was carried out with a sulfonic acid-modified mesostructured catalyst. This catalyst has yielded fatty acid methyl ester (FAME) purity over 95 wt % for oil conversion close to 100% under best reaction conditions (temperature 180 degrees C, methanol/oil molar ratio 10, and catalyst loading 6 wt % with regard to the amount of oil). Interestingly, high methanol concentration leads to a detrimental effect on the catalyst activity. Regardless of the presence of free fatty acids, the sulfonic acid-modified mesostructured catalyst showed high activity toward simultaneous esterification and transesterification. These sulfonated mesostructured materials are promising catalysts for preparation of biodiesel, but some aspects related to the tuning of the adsorption properties of the silica surface and the enhancement of the catalyst's reusability must be addressed in future work.