Under homogeneous conditions and as a Y zeolite supported complex, manganese(III) tetra(4-N-benzylpyridyl)porphyrin (MnTBzPyP) is an active catalyst in the epoxidation of (R)-(+)-limonene and alpha-pinene, and in the hydroxylation of carvacrol and thymol, using H2O2/ammonium acetate, at room temperature and atmospheric pressure. A combined study on the characterization and catalytic performance of MnTBzPyP-NaY suggests that its preparation led to a successful inclusion of MnTBzPyP inside the zeolite during the hydrothermal synthesis. Unfortunately, irreversible catalyst deactivation occurs in the presence of H2O2. Changes in the crystalline structure of MnTBzPyP-NaY during the oxidative transformations are accompanied by leaching of the porphyrin complex to the reaction solution, accounting for the nearly complete loss of activity when the catalyst is re-used. Higher substrate conversions were achieved with the zeolite-impregnated complex. The iron analogue is inactive, under the applied reaction conditions. (C) 2003 Elsevier Science B.V. All rights reserved.