The formation of volatile products is essential in dry etching reactions. Pt compounds have a low vapor pressure and thus Pt is hardly removed by dry etching. In the present work, Pt thin films were etched in supercritical CO2 fluids. Hexafluoroacetlyacetone (Hhfac), a fluorinated compound, was added to a supercritical CO2 fluid together with O2 at elevated temperatures (typically 220 °C). Etching was observed only when O2 was added. The etching amount increased with either reaction temperature, O2 concentration, or Hhfac concentration. The etching rate at 220 °C was approximately 0.1 nm/min.