For a cylindrical catalyst pellet, a study is presented concerning four important aspects of the interaction between internal diffusion and reaction processes. Effective diffusivities, shown by experimental results, are essentially identical under gas reaction and nonreaction conditions no matter whether the surface is poisoned or unpoisoned. For effectiveness factor, an approximate analytical expression, with a maximum deviation of less than 1.5% from analytical solutions or numerical calculation results, is proposed for arbitrary kinetics. Multiplicity features for a cylindrical pellet, according to direct calculation, are shown to be analogous to those of a spherical pellet. Finally, Thiele modulus is found to be a key parameter in determining the unsteady-state behaviors of a cylindrical catalyst pellet.