The sintering of sputter‐produced, silica‐supported platinum thin films was studied using electron microscopy and x‐ray diffraction following treatments in both reactive (ethylene oxidation—O2+C2H4) and nonreactive atmospheres (vacuum, O2, N2, C2H4, CO2, H2O). Sintering behavior in nonreactive atmospheres (thermal sintering) was found to be insensitive to the gas phase and was a function of temperature only. Changes in film structure following thermal sintering were not dramatic and were readily explained by conventional models. In contrast, sintering in reactive atmospheres was found to be a strong function of temperature and the O2/C2H4ratio. Over a relatively narrow temperature range (770–970 K), the surface was found to be dramatically restructured with plantinum completely stripped from some areas and large particles forming in others. This type of sintering (reaction‐enhanced sintering) possibly results from the interaction of homogeneously formed radicals with the metal surface to form metastable mobile intermediates.