1-Methylnaphthalene (1-MNa) thermal decomposition was studied in a batch reactor ( gold tube) submitted to a constant pressure (100 atm), at various temperatures from 380 to 450 C and for residence times in the range 1-72 h. Pyrolysis effluents were recovered by two successive solvent extractions: first in n-pentane and then in dichloromethane. Light compounds and gaseous effluents were identified and quantified by gas chromatography, while the amount of heavier compounds was determined by weight. Study at low conversion of 1-MNa thermal cracking, below 2%, showed that the rate of decomposition of 1-MNa was accelerated by the formation of dimethylbinaphthalenes. 1-MNa was mostly converted into naphthalene, methylated dimers, methane, and hydrogen gas. Above 10% conversion, the secondary products were dimethylnaphthalenes, 2-methylnaphthalene, and heavier dehydrogenated polyaromatics. The global conversion (10-80% conversion) of 1-methylnaphthalene was correctly modeled by a first-order law with respect to the reactant, with rate constants depending on temperature according to the Arrhenius law. Correspondingly, the apparent kinetic parameters derived from the experimental data were E) 47.4 kcal mol(-1) and A) 10(9.9) s(-1). These results were in good agreement with those obtained on heavier methylated polyaromatics. Hence, data generated from this work supported the assumption that there may exist one general kinetic model accounting for the thermal cracking of methylated polyaromatics in HP/HT reservoir conditions. Therefore, a reaction pathway for the thermal decomposition of methylated polyaromatics was elaborated on the basis of the free-radical mechanisms proposed previously in the literature and explaining the formation of the main products.