Low-pressure (4.0 kPa) premixed laminar 2,5-dimethylfuran (DMF)/oxygen/argon flame with an equivalence ratio of 2.0 was Studied with tunable vacuum ultraviolet (VUV) synchrotron radiation photoionization and molecular-beam mass spectrometry. Photoionization mass spectra of DMF/O-2/Ar flame were recorded and the photoionization efficiency Curves of the combustion intermediates were measured. Flame species, including isomeric intermediates, are identified by comparing the measured ionization energies with those reported in literatures or those calculated with Gaussian-3 procedure. More than 70 species have been detected, including furan and its derivatives, aromatics, and free radicals. Possible reaction pathways of DMF, 2-methylfuran, and furan are proposed based on the intermediates identified. DMF can be consumed by H-abstraction and pyrolysis reactions. 2-Methylfuran and furan can be consumed by H-abstraction, H-addition and pyrolysis reactions. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.