Fe bulk specimen have been treated with phosphoric acid in order to obtain a conversion surface layer and the oxidation resistance has been studied by means of in situ thermogravimetric experiments in artificial air (20% O-2; 80% N-2). For oxidation time of 48 h at 400 degreesC it shows an important decrease of the oxidation kinetic in comparison with alpha-Fe. Moreover, the kinetic can be described by two successive parabolic stages. This behaviour is respectively related to an X-ray photoelectron spectroscopy (XPS) analysis of the surfaces and to previous results obtained on the oxidation of a-iron. (C) 2002 Elsevier Science B.V. All rights reserved.