For a better understanding of the chemistry involved during the combustion of components of diesel fuel, the structure of a laminar lean premixed methane flame doped with n-propylcyclohexane has been investigated. The inlet gases contained 7.1% (molar) methane, 36.8% oxygen, and 0.81% n-propylcyclohexane (C9H18) corresponding to an equivalence ratio of 0.68 and a ratio C9H18 / CH4 of 11.4%. The flame has been stabilized on a burner at a pressure of 6.7 kPa (50 Torr) using argon as diluent, with a gas velocity at the burner of 49.2 cm/s at 333 K. Quantified species included usual methane C0-C2 combustion products, but also 17 C3-C5 hydrocarbons, 7 C1-C3 oxygenated compounds, as well as only 4 cyclic C6+ compounds, namely benzene, 1,3-cyclohexadiene, cyclohexene, and methylenecyclohexane. A new mechanism for the oxidation of n-propylcyclohexane has been proposed. It has allowed the proper simulation of profiles of most of the products measured in flame, as well as the satisfactory reproduction of experimental results obtained in a jet-stirred reactor. The main reaction pathways of consumption of n-propylcyclohexane have been derived from rate-of-production analysis.