AbstractSynthetic zeolites were studied in order to investigate their ability to encapsulate and to release drugs. In particular, a zeolite X and a zeolitic product obtained from a cocrystallization of zeolite X and zeolite A were examined. These materials were characterized by chemical analyses (ICP‐AES), X‐ray diffraction, nitrogen adsorption isotherm, scanning electron microscopy, laser diffraction, and infrared spectroscopy. Since ketoprofen was chosen as a model drug for the formulation of controlled‐release dosage forms, it was encapsulated into these two types of synthetic zeolites by a soaking procedure. Drug‐loaded matrices were then characterized for entrapped drug amount and thermogravimetric behavior. In both types of activated zeolites, the total amount of ketoprofen (800 mg) was encapsulated in 2 g of matrix. By using HPLC measurements, ketoprofen release studies were done at different pH conditions so as to mimick gastrointestinal fluids. The absence of release in acid conditions and a double phased release, at two different pH values (5 and 6.8), suggest that after activation these materials offer good potential for a modified release delivery system of ketoprofen. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008