The improvement of the thermal oxidizers commonly used in the industry to treat the gaseous effluents and thus to limit the rejection of pollutants in the atmosphere requires knowledge of the oxidation processes of volatile organic compounds (VOCs). Methylethylketone (MEK) is a representative VOC and it has been chosen also because of the lack of kinetic data available in the literature concerning the ketones oxidation. Premixed laminar stoichiometric CH4/MEK/O-2/N-2 flat flames have been studied at low-pressure by varying the percentage of seeded MEK up to 3%. The experimental measurements, obtained by coupling microprobe sampling with gas chromatography-mass spectrometry (GC/MS) analysis, have been compared with the predictions of a detailed mechanism. The developed mechanism includes 29 oxygenated species involved in 140 reversible reactions specific to the MEK thermal degradation: it takes into account the first steps of the MEK oxidation and the oxidation processes of the main oxygenated intermediate compounds as acetone, methanol, ethanol, acetaldehyde and propanal. When the quantity of MEK added to the methane flame varies, the increase of C-2 and C-3 hydrocarbon species and the evolution of oxygenated intermediates are well reproduced by the model. The sensitivity analysis points out the main reactional pathways involved in the thermal degradation of MEK in flame conditions and reveals the important production of methyl and ethyl radicals which lead, by recombination processes, to the formation of the oxygenated intermediate compounds.