In this study, the construction of a highly negatively charged layered material [CH3CH2NH3]6In6S12 (InS-1) by introducing a lacunary cluster as the building block is reported. The pronounced framework negative charge density (5.59 × 10-3) and the soft Lewis basic S component endow InS-1 with an effective ion exchange performance toward heavier Sr2+, with a top-level adsorption capacity qm of 105.35 mg g-1. InS-1 exhibits a good exchange activity over pH 3-12, and the Sr2+-laden product can be facilely eluted.