Periodic operation of NO-CO reaction over Pt/Al2O3 was conducted by using an egg-shell-type catalyst and an egg-white-type catalyst in order to investigate the effect of intraparicle diffusion on the reaction performance. The former catalyst held platinum in the outer layer of the particle and the latter held in the inner layer. Time averaged conversion of NO under periodic operation exceeded that under steady operation in a certain range of periods, showing a maximum versus period for both catalysts. In the case of the egg-white-type catalyst, the conversion rose and declined with a lasser dependence on the period than in the case of the egg-shell-type catalyst. Under periodic operation with periods up to 360 s, the egg-white-type catalyst showed reaction performance higher than that under steady operation, A model calculation reproduced the tendency and revealed that intraparticle diffusion slowed the rate of desorption of CO, and that the slow desorption of CO resulted in the experimental observation for egg-white-type catalyst.