Removal of ammonium cations from aqueous solution was investigated using an arene-sulphonic acid functionalised mesostructured SBA-15 material as adsorbent. Arene-sulphonic acid-SBA-15 (AS-SBA-15) was prepared via a co-condensation strategy using tetraethylorthosilicate (TEOS) and 2-(4-chlorosulphonylphenyl)ethyltrimethoxysilane (CSPTMS) as framework precursors under acidic conditions. The material exhibited high surface area (680 m2/g) and total pore volume (0.84 mL/g). The effects of adsorbent loading, initial ammonium concentration, temperature, pH and the presence of competitive ions on the adsorption performances were investigated. The ammonium removal increased with the increase of the adsorbent loading and the decrease of the initial concentration. The adsorption capacity decreased with increasing the temperature. Maximum adsorption capacity obtained at 5°C was ca. 19 mg NH/g adsorbent. The isotherms data were studied using different adsorption models and thermodynamic parameters were calculated. Competitive ions such K+ and Na+ slightly affected the ammonium adsorption. After six adsorption–desorption cycles, the adsorbent retained its adsorption capacity.