The oxidation kinetics of epsilon-Fe2N1-x, subjected either to a sputter cleaning pretreatment or a sputter cleaning and an additional annealing pretreatment, at P-O2 = 1 x 10(-4) Pa and at temperatures ranging from 300 to 500 K, was investigated with ellipsometry. The initial oxidation rate of sputter cleaned + annealed epsilon-Fe2N1-x was observed to be lower than of sputter cleaned epsilon-Fe2N1-x, but upon prolonged oxidation sputter cleaned + annealed epsilon-Fe2N1-x attained a higher oxidation rate than sputter cleaned epsilon-Fe2N1-x. The oxidation kinetics was interpreted using the model due to Fromhold and Cook wherein cation and electron currents in the growing oxide film are coupled. The effect of the nitrogen concentration in the iron-nitride substrate on the oxidation kinetics could be discussed in terms of this model and related to the morphology and phase constitution of the oxide film.