An ethylammonium-templated indium sulfide, [CH3CH2NH3]6In8S15 (InS-2), featuring anionic layers perforated with large, 24-membered rings that facilitate the accommodation of hydrated Sr2+ ions is reported. InS-2 exhibits an excellent adsorption performance toward Sr2+ with a top-ranked capacity (qm = 143.29 mg g-1), rapid kinetics, wide pH durability (3-14), β- and γ-radiation resistances, and a facile elution.