An in situ, one-step encapsulation methodology has been applied to the preparation of caffeine ordered (CAF@SBA-15) and non-ordered (CAF@silica) mesoporous silicas. This consists of adding the target organic compound to the precursor silica sol, in the presence of a triblock copolymer template in the case of ordered silica, to achieve mesoporous materials. Caffeine encapsulation was assessed by thermogravimetry, infrared spectroscopy and release experiments. The caffeine-block copolymer surfactant interaction by van der Waals forces produced micelled caffeine in the case of CAF@SBA-15. The formation of hydrogen bonds between caffeine groups and silica hydroxyls (in the case of both ordered and non-ordered silicas) was responsible for the thermal stability and drug release improvements achieved. CAF@SBA-15 showed a higher amount of caffeine encapsulated (23 wt%) than CAF@silica (20 wt%) due to the existence of micelled caffeine. Micelled caffeine was quickly released from CAF@SBA-15, while the complete release of all the caffeine occurred in about half a day due to adsorption on the pore wall silica. CAF@silica released caffeine during 1 day. (C) 2013 Elsevier B.V. All rights reserved.