The thermal decomposition of F2O was studied in a single-pulse shock tube over the temperature range 770-1390°K. For temperatures below 1000°K these results are in excellent agreement with the previous shock tube data; however, all rates obtained by conventional techniques, either in static or in flow systems, prove to be higher than those derived from the shock tube techniques. This is attributed to surface effects which cannot be avoided in conventional systems. Our present data are accounted for by the following scheme; F2O + Ar ⇌ F + OF + Ar (1, –1), 20F⇅2F + O2(2), 2F + Ar⇌ F2+ Ar(3, -3), with k1 = 1017.3±1.0e-(42.5±4.1)/RTcc/mole sec and k2 = 1012-10±0.12 cc/mole sec. The reverse reactions (–1) and (–3) cannot be neglected even in the early stages of reaction. The bond dissociation energy, D(FO-F), was found to be 42.7 ±4.1 kcal/mole, on the basis of the RRKM theory. The mechanism of the F2O2 decomposition is also discussed.