Pt-PtOx thin films were prepared on Si(100) substrates at temperatures from 30 to 700 degreesC by reactive r.f. magnetron sputtering with platinum target. Deposition atmosphere was varied with O-2/Ar flow ratio, The deposited films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. Resistively of the deposited films was measured by d.c. four probe method. The films mainly consisted of amorphous PtO and Pt3O4 (or Pt2O3) below 400 degreesC, and amorphous Pt was increased in the film as a deposition temperature increased to 600'C. When deposition temperature was thoroughly increased, (111) oriented pure Pt films were formed at 700 degreesC. Compounds included in the films strongly depended on substrate temperature rather than O-2/Ar flow ratio. Electrical resistivity of Pt-PtOx films was measured to be from the order of 10(-1) Omega cm to 10(-5) Omega cm, which was related to the amount of Pt phase included in the deposited Films.