Small-angle X-ray scattering profiles of the ethylene and styrene ionomers were Studied to clarify the structure of ionic aggregates as a functions of the nature of cations, acid content, and degree of neutralization. The ionic cluster peak was observed for the ionomers with a certain degree of neutralization. The scattering profile of the ionic cluster peak was analyzed by the modified hard-sphere model proposed by Yarusso and Cooper, and the size of ionic aggregates, closest approach distance between the aggregates, and average system volume per ionic aggregate were obtained. The size and distance of the ionic aggregates in the ionomers with monovalent cation, sodium and potassium cations, increased with the ion content (acid content x degree of neutralization), while those with divalent one, zinc and copper cations, and trivalent one, ferric cation, changed only slightly. The number of cations in an ionic aggregate was evaluated in an approximate manner by using the average system volume per ionic aggregate and the density of ionomer or the size of the ionic aggregate and the density of the ionic aggregate estimated by a simple additivity rule for each phase.