We have carried out a detailed and systematic study to derive a quantitative understanding for the mechanism of the liquid-phase reaction of methylcyclopentane on ZSM-5 catalyst in a stirred batch reactor and at five temperatures between 110 and 175degreesC. The rate constants (k) and catalyst deactivation (k(d)) were obtained on the basis of the cyclohexane by a ring-expansion of methylcyclopentane with the selectivity of 92% or over. The rate of deactivation of ZSM-5 is as large as about 100 times of an activation rate. The activation parameters for the isomerization of methylcyclopentane are DeltaH(double dagger) = 11.87 kcal/ mol and DeltaS(double dagger) = -55.9 cal/(mol K). As the conversion increases, the yields of 2-methylpentane and cyclohexane are linearly increased, but those of 3-methylpentane and C-5- are sharply and nonlinearly increased. The scheme of methylcyclopentane reaction over ZSM-5 is as follows: MCP --> CH (main reaction) or 2-MP --> 3-MP or C-5-. Higher reaction temperature favors cracking reaction (ring opening or cracked micromolecules) against the isomerization by a ring expansion.