The adsorption of As(V) ions from aqueous solution onto treated granular zeolitic tuff (TZT) has been investigated. In this study, the effects of adsorbent dose, solution pH, initial concentration, contact time, and temperature were examined. Thermodynamic analysis revealed that the adsorption behavior of As(V) ions onto the TZT adsorbent was an endothermic process, resulting in higher adsorption capacities at higher temperatures. Thermodynamic parameters, the negative values of Delta G(o) and positive values of Delta H(o), revealed that the adsorption process was spontaneous and endothermic. The Langmuir and Freundlich isotherm models were employed to fit the isothermal adsorption. The results revealed that the Langmuir isotherm model is the best-fit model to predict the experimental data.