The pyrolysis of 2,5-dimethylfuran (DMF) in a flow reactor was investigated at various pressures (30, 150 and 760 Torr) by synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Dozens of pyrolysis products, especially a series of radicals and aromatics, were identified from the measurement of photoionization efficiency spectra; and their mole fraction profiles were measured at 780-1470 K. Phenol, 1,3-cyclopentadiene, 2-methylfuran, vinylacetylene and 1,3-butadiene were observed with high concentrations in the decomposition of DMF. The pressure-dependent rate constants of the major unimolecular decomposition reactions of DMF were theoretically calculated, and was adopted in the pyrolysis model of DMF with 285 species and 1173 reactions developed in the present work. The model was validated against the species profiles measured in both the present work and the previous pyrolysis studies of DMF. Based on the rate of production and sensitivity analyses, main pathways in the decomposition of DMF and the growth of aromatics were determined. The unimolecular decomposition to produce CH3CHCCH and acetyl radicals, H-atom abstraction to produce 5-methyl-2-furanylmethyl radical, ipso substitution by H-atom to produce 2-methylfuran and H-atom attack to produce 1,3-butadiene and acetyl radical were concluded to dominate the primary decomposition of DMF. Further decomposition of 5-methyl-2-furanylmethyl radical leads to great production of phenol and 1,3-cyclopentadiene which can be readily converted to precursors of large aromatics such as cyclopentadienyl radical, phenyl radical and benzene. As a result, the formation of aromatics in the pyrolysis of DMF is promoted compared with the pyrolysis of cyclohexane and methylcyclohexane under very close conditions. This observation implies the potentially high sooting tendency of DMF, and emphasizes the necessity to investigate the sooting behavior and soot formation mechanism in DMF combustion for the potential application of DMF as an alternative engine fuel. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.