The rate constants for the epoxidation of styrene by six oxoiron(IV) porphyrin cation radicals 1-X (X = -F, HOCH3, -Cl, -OAc, -OSO2CF3, -OClO3) which differ only in the identity of their axial ligan were obtained under conditions where the presence of the axial ligands during the reactions could be ascertained. A qualitative relationship was found between the field strengths of the ligands and their pronounced effect on the reactivity of 1-X.