The Teminan bentonite deposit is located in ~25 km southwest of Naeen, Isfehan Province. This deposit has layered and massive form and is an alteration product of tuff breccias of Oligo-Miocene age. Mineralogical data show that montmorillonite, heulandite, clinoptilolite, quartz, anorthite, orthoclase, calcite, beidellite, illite, and microcline are the principal rock-forming minerals in this deposit. Distribution pattern of REEs normalized to chondrite indicate an intense differentiation of LREEs from HREEs accompanied by occurrence of negative Eu anomaly during bentonitization. Geological data suggest that the alteration processes of tuff breccias to bentonite in this area occurred in an open system, and leaching and fixation processes were two principal regulating factors in concentration of most trace and rare earth elements. By considering the obtained results, it seems that acidic pH and its variation degree, adsorption, inhomogeneity of parent rock composition, incorporation in crystal lattice, difference in degree of complexation with sulfate, chloride, and fluoride ligands, diagenesis, ionic exchange, residual concentrations, and difference in degree of stability of minerals against alteration are the key controlling factors for distribution of elements during evolution of the Teminan bentonite deposit.