The imidazole-modified silica (Silm) was used for immobilization of octabromotetraphenylpor-phyrinatomanganese(III) chloride, Mn(Br8TPP)Cl and tetraphenylporphyrinatomanganese(III) chloride, Mn(TPP)Cl. Silm is not only a heterogeneous axial base but also a support for immobilization of manganese porphyrins. [Mn(Br8TPP)Cl-Silm] and [Mn(TPP)Cl-Silm] as biomimetic oxidation catalysts catalyze alkene epoxidation and alkane hydroxylation with NaIO4 under agitation with magnetic stirring. Ultrasonic irradiation enhanced the catalytic activity of these catalysts in alkene epoxidation and alkane hydroxylation and this led to shorter reaction times and higher product yields. These new heterogenized catalysts could be reused several times without significant loss of their catalytic activity. (C) 2008 Elsevier B.V. All rights reserved.