Gas-phase hydrogenation of mesitylene to cis- and trans-1,3,5-trimethylcyclohexane was studied in a differential microreactor at atmospheric pressure and 418-493 K over an Ni/Al2O3 catalyst. Rapid reversible deactivation of the freshly reduced catalyst prompted reactivation before every kinetic measurement and extrapolation of the steady state activity to initial activity. Reaction orders were close to zero for mesitylene and ranged from 0.6 (418 K) to 2.0 (493 K) for hydrogen. A rate maximum for the production of the saturated compounds was observed at about 450 K, Varying with the pressure ratio of the reactants. The results were in line with previously reported results on xylene hydrogenation.