Ignition delay times for 1% cyclopentane/O-2 and 0.833% methylcyclopentane/O-2 mixtures diluted by argon were measured behind reflected shock waves at pressures of 1.1 and 10 atm, with equivalence ratios of 0.577, 1.0, and 2.0, and in the temperature range from 1150 to 1850 K. Submechanisms for cyclopentane and methylcyclopentane were developed and added to the JetSurF2.0 mechanism for the kinetic interpretation of cyclopentane and methylcyclopentane oxidation chemistry at the high temperature region. Simulations with the model exhibit fairly good agreements with the measured ignition delay times of both cyclopentane and methylcyclopentane under all tested conditions. Cyclopentane shows longer ignition delay time than methylcyclopentane, especially for the fuel-lean mixture. Reaction pathways and sensitivity analyses were conducted to get insights into the oxidation process of cyclopentane and methylcyclopentane. Then, three factors are given for the effect of a cyclic ring and substitution of a methyl group. Substitution of a methyl group weakens the C-C bond to motivate fuel unimolecular decomposition. The shape of the cyclic ring determines the chain alkyl radicals, affecting regeneration and accumulation of H radical. The presence of a methyl group also leads to different alkyl radicals.