A layered clay mineral, tetrasilicicfluormica intercalated with spherical, planar, and rodlike alkylammonium ions, was prepared. Two-dimensional dynamic properties of intercalated ions were investigated by solid-state H-1 and H-2 NMR and electrical conductivity measurements. From these measurements, all intercalation compounds were revealed to show two-dimensional (2-D) cationic self-diffusion between mica layers. The 2-D self-diffusion could be characterized by comparing shapes of intercalated ions and their occupancies in the interlayer space. The activation energies for the 2-D self-diffusion in the present intercalation compounds were found to be smaller than those for three-dimensional cationic diffusion in bulk crystals.