Platinum particles supported on a sulfate ion-treated zirconium oxide (SO:--ZrO*) were characterized by means of X-ray absorption near edge structure (XANES) /extended X-ray absorption fine structure (EXAFS) and temperature-programmed reduction (TPR) in order to elucidate the nature of the sulfur-aided metal-support interactions. X-ray edge shift and area calculation, which give the number of unoccupied d states of the platinum particles, are suggestive of electron transfer from the platinum particle to the support and/or existence of the platinum unreduced cations. Fourier transforms (FTs) of /?-weighted EXAFS reveal that the Pt particles on the SO:--ZrO, support after hydrogen treatment at 623 K are a mixture of Pt metal ( Pt-Pt bond length = 2.77 A) and Pt oxides, whereas the Pt particles on ZrO, exist as metal (Pt-Pt bond len@h = 2.73 A). TEM reveals that the presence of sulfate ion causes an increase of the Pt particle size (30 A-50 A). The low reducibility of the Pt particles on the SO,'--ZrO, support is evidenced by TPR results. The nature of the platinum-support interaction in the Pt/ SO:--ZrQ catalyst is understood in terms of a Redox (reduction-oxidation) metal-support interaction.