The thermal reactions of 2,5-dimethylfuran were studied behind reflected shock waves in a pressurized driver single pulse shock tube over the temperature range 1070-1370 K and overall densities of similar to 3 x 10(-5) mol/ cm(3). A large number of products resulting from unimolecular cleavage of the ring and consecutive free radical reactions were obtained under shock heating. A methyl group migration from C(2) to C(3) in the ring with the elimination of CO produces four isomers of C5H8 in unimolecular processes. An additional unimolecular process is the decomposition of 2,5-dimethylfuran to CH3CO and C4H5 which is an important initiator of free radical reactions. Ejection of a hydrogen atom from the methyl group in the molecule is another channel for initiation of free radical reactions in the system. The 2,5-dimethylfuryl radical, which is obtained in the process of II-atom ejection, decomposes in channels similar to those of 2,5-dimethylfuran to produce, among other products, C5H7, which is the precursor of cyclopentadiene. The major decomposition product found in the post shock mixtures is carbon monoxide. The rate constant of its overall formation is estimated as k(CO) = 10(15.81) exp(-75.1 x 10(3)/RT) s(-1) where R is expressed in units of cal/(K mel). Other products that were found in the postshock samples in decreasing order of abundance were C4H4, C2H2, and CH4 in roughly the same abundance, C2H4, C2H6, CH2=CH-CH=CH2, cyclopentadiene p-C3H4, and a-C3H4 and 2-methylfuran. Other isomers of C4H6, C5H6 and C5H8, and some additional products were found in very small quantities. The total decomposition of 2,5-dimethylfuran in terms of a first-order rate constant is given by: k(total) = 10(16.22)exp(-77.5 x 10(3)/RT) s(-1). An oxygen-carbon mass balance among the decomposition products is obtained. A reaction scheme composed of 50 species and some 180 elementary reactions accounts for the product distribution over the temperature range covered 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 computer simulation and sensitivity analysis are shown. Differences and similarities among the reactions of furan, 2-methylfuran, and 2,5-dimethylfuran are discussed.