A difference of kinetics between powdered and pelletized catalysts for the reaction system obeying Lagmuir-Hinshelwood (L-H) type kinetics was experimentally and theoretically demonstrated. Liquid-phase hydrogenation of 1-methylnaphthalene (I-MN) was performed as a model reaction of hydrogenation of highly aromatic diesel oil feed stock. Using two types of batch autoclave reactors, kinetic data were obtained with powdered, cylindrical and trilobed commercial Co-Mo/gamma-Al2O3 catalysts, in the range of 583-623 K temperature(T) and 5.0 - 8.0 MPa total pressure (P), with feed liquids of Ia and 30 wt% initial concentration of 1-MN (F-MN) diluted in a C-14-C-16 normal paraffin mixture. The inhibition effect of 1-MN was clearly observed for the powdered catalyst. L-H type intrinsic kinetic equations including inhibition terms of hydrogen and I-MN were established. On the other hand, the reaction with the pelletized catalysts behaved as a pseudo first order one with respect to the concentration of I-MN in the case of lower F-MN. A kinetic model - a combination of intrinsic kinetics and intraparticle mass balance - with a tortuosity factor of 3.1 excellently represented the difference of kinetics, as well as the effect of T, P, F-MN and size and shape of catalyst, on the product yields over the pelletized catalysts. The difference of kinetics was also theoretically explained from the view of the contribution of intraparticle diffusion effects.