An oxidative enzyme, horseradish peroxidase (HRP), was immobilized on phosphorus- and/or calcium-modified MCM-41 mesoporous silicas with suitable pore diameters. Structural analyses by means of XRD and nitrogen adsorption confirmed that the P- and/or Ca-modified MCM-41 materials retained their structural quality even after the modification or the enzyme immobilization. Detailed studies of the adsorption behaviors and characterization using FT-IR spectroscopy and zeta potential measurements revealed that the P and Ca atoms attached on the silica surface provided increased uptake of HRP molecules, which is attributable to the more 8 o negatively charged surface or strong interatomic interactions between these atoms and the functional groups of the enzyme. In particular, P-modified MCM-41 showed an improved adsorption capacity in g short adsorption period and over a wide pH range without denaturation of the protein structure, in which the largest HRP adsorption capacity was 154 mg/g. Furthermore, HRP immobilized on P-modified MCM-41 showed higher enzymatic activity and reusability in the oxidation of 1,2-diaminobenzene in an organic solvent at a temperature of 37 degrees C than that immobilized on the parent MCM 41 This enhancement in enzymatic activity can be related to the structural integrity of loaded HRP molecules and the stfong adsorption on the P-MCM-41 surface. This work thus demonstrates that mesoporous silica bearing P and/or Ca atoms can provide a surface environment suitable for enzyme immobilization.