The catalytic activities of stoichiometric and lean mixture simulated exhaust from automotive engines have been investigated on bimetallic Pt/Fe/Al2O3 catalysts after the O-2, O-2-H-2, and O-2-H-2-O-2 treatments and compared to that of Pt/Al2O3 catalysts. The state of the Pt particles of the Pt/Fe/Al2O3 catalysts was also investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). The activity of the Pt/Fe/Al2O3 catalyst was greater than that of the Pt/Al2O3 catalyst after the O-2-H-2-O-2 treatment for the stoichiometric mixture. Also, the activity of the Pt/Fe/Al2O3 catalyst after the O-2-H-2 treatment was greater than that after the O-2 and O-2-H-2-O-2 treatments. Pt particles were found to react with Fe additives to form homogeneous Pt-Fe alloy particles on Al2O3 under reducing conditions. Also, the Pt-Fe alloy particles on Al2O3 were found to segregate into Pt and Fe2O3 and to form a Fe2O3 coverage layer on Pt particles so that Pt particles were prevented from sintering when heated at 800 degrees C for a lean mixture. On the other hand, the activity of the Pt/Al2O3 catalyst was greater than that of the Pt/Fe/Al2O3 catalyst after the O-2-H-2-O-2 treatment for lean mixture. The layer of Fe2O3 on Pt is responsible for the low activity.