One-electron reduction of mononuclear nonheme iron(III) hydroperoxo (Fe(III) OOH) and iron(III) alkylperoxo (Fe(III) OOR) complexes by ferrocene (Fc) derivatives resulted in the formation of the corresponding iron(IV) oxo complexes. The conversion rates were dependent on the concentration and oxidation potentials of the electron donors, thus indicating that the reduction of the iron(III) (hydro/alkyl)peroxo complexes to their one-electron reduced iron(II) (hydro/alkyl)peroxo species is the rate-determining step, followed by the heterolytic OO bond cleavage of the putative iron(II) (hydro/alkyl)peroxo species to give the iron(IV) oxo complexes. Product analysis supported the heterolytic OO bond-cleavage mechanism. The present results provide the first example showing the one-electron reduction of iron(III) (hydro/alkyl)peroxo complexes and the heterolytic OO bond cleavage of iron(II) (hydro/alkyl)peroxo species to form iron(IV) oxo intermediates which occur in nonheme iron enzymatic and Fenton reactions.