High-valent iron-oxo species have been frequently em-ployed in heme and nonheme iron enzymes to carry out catalytic oxygenation reactions. 1-11 In heme-based systems, biological and synthetic oxoiron(IV) porphyrin π-cation radicals are believed to carry out the catalytic oxidations of organic substrates. In the nonheme iron enzymes, oxoiron(IV) intermediates have recently been identified by spectroscopic methods in the catalytic cycle of taurine dioxygenase, and synthetic nonheme oxoiron(IV) species bearing tetradentate and pentadentate ligands were also isolated and characteriz-ed. 12-18 In addition, it has been demonstrated that the non-heme oxoiron(IV) species were capable of conducting the conversion of diverse organic subsatrates such as PPh 3 , thioanisole, alcohol, and alkanes. 18-20 The molecular mechanisms of oxidative N-demethylation of N,N-dimethylanilines by heme enzymes such as per-oxidases and cytochrome P-450 have been studied for the past twenty years. However, two possible mechanisms, electron transfer followed by proton transfer and hydrogen transfer from α-C-H bonds of the methyl group in N,N-dimethylanilines, are still under debate. Recently, we also reported the oxidative N-dealkylation of N,N-dialkylanilines and demonstrated that the oxidative N-dealkylation reactions occurred via a proton-coupled electron transfer process. 21 Meanwhile, secondary amine substrates bearing a cyclo-propyl group have been used in the relation to a mechanism-based inactivation of heme enzymes, and the formation of a highly reactive carbon-centered radical was reported in the oxidation of heteroatom-containing cyclopropyl sub-strates. 22-27 Relatively, a few studies for the oxidation of N-methylanilines as substrate were reported using iron, cobalt, and copper complexes. 28-30 However, no detailed mechanis-tic study in the oxidation of secondary amines with non-heme Fe(IV)-oxo species has been reported until now. Presented in this study is a kinetic examination of the oxidation of N-methylanilines with [(tmc)Fe IV =O] 2+ (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), which yields N,N'-dimethyl-N,N'-diphenylhydrazine formed by the coupling of two N-methylaniline molecules. By deter-mining the rate constants for the step of electron transfer from N-methylaniline to the iron(IV)-oxo species, we sug-gest that the oxidation of N-methylaniline occurs via an electron transfer.