The thermal reactions of propylene oxide (1,2-epoxypropane) were studied behind reflected shocks in a pressurized driver single-pulse shock tube over the temperaturee range 850-1250 K and overall densities of similar to 3 x 10(-5) mol/cm(3). Four isomerization products, acetone, propanal, methyl vinyl ether, and allyl alcohol, and a large number of decomposition products were obtained under shock heating. The major decomposition products in decreasing order of abundance were CO, C2H4, C2H6, and CH4. Studies with free-radical scavengers and with isotopically labeled reactant (C3D6O) indicated that the isomerization products and ethylene retain the original skeleton of the reactant whereas all the other products involve free-radical reactions. It is believed that the free-radical reactions, as in the decomposition of ethylene oxide, are initiated by decomposition of thermally excited isomerization products prior to losing their energy by collisions. The rate constants obtained for the isomerization reactions are in very good agreement with the values extrapolated from low temperatures but are by a factor of 7-10 higher than the high-temperature rate constants obtained recently by Qin et al. A reaction scheme composed of 37 species and 68 elementary reactions accounts for the product distribution over the temperature range used in this study. First-order Arrhenius rate parameters for the formation of the various reaction products are given, a reaction scheme is suggested, and results of the computer simulation and the sensitivity analysis are shown. Differences and similarities between the reactions of ethylene oxide and propylene oxide are discussed.