The sulfoxides of penicillin derivatives are important pharmaceutical intermediates and can be prepared by air oxidation of corresponding sulfides catalyzed by cobalt(III) acetylacetonate (Co(acac)(3)). However, when using the homogeneous catalyst, it is very difficult to separate the catalyst from product, which makes it impossible to reuse the catalyst directly. While the heterogeneous Co(acac)(3) encapsulated by sol-gel method can solve the problem. They have high selectivity and activity. They are leach proof and can be recycled in numerous runs. The sol-gel precursor can be tetraethoxysilane (TEOS) or tetrabutyl titanate (TBOTi) or triisopropyl aluminate (TIOAl). FT-IR and N-2 adsorption was employed to characterize the sol-gel catalyst. HPLC was used to analyze the conversion of penicillin derivatives. (C) 2003 Elsevier Science B.V. All rights reserved.