The effects on solid-catalyzed reaction of intraparticle flow resulting from an axial pressure gradient in a flow reactor are investigated theoretically and experimentally. First, an equation which gives the effectiveness factor under the combined effects of flow and diffusion is presented and the results are compared with experiments using an ion exchange reaction. From the analyses the large effects of intraparticle flow on reaction are proved, and it is found that a packed bed of catalyst pellets permitting intraparticle flow is the most suitable reactor for reducing reactor volume and flow resistances.