<p>Radiostrontium remediation is crucial for ecological protection and sustainable development of nuclear energy. However, efficient removal of ⁹⁰Sr from complex radioactive liquid waste, especially under acidic conditions, remains challenging due to material instability and intense proton competition. Herein, the rapid and highly selective capture of Sr²⁺ in neutral and even acidic solutions has been achieved by a layered potassium phosphatoantimonate KSbP₂O₈ with excellent radiation and thermal stability. Under neutral conditions, it possesses high maximum adsorption capacity (<i>q</i>_<i>m</i>^Sr = 110.25 mg g⁻¹), rapid adsorption kinetics (the removal rate (<i>R</i>^Sr) of 91.54% within 30 min), and excellent selectivity for Sr²⁺, and facile regeneration. Particularly, even under acidic conditions (pH 2.0), KSbP₂O₈ still maintains excellent Sr²⁺ removal capacity (<i>q</i>_<i>m</i>^Sr = 79.38 mg g⁻¹), fast kinetics, and high selectivity. A mechanism study by multiple characterizations reveals that the efficient Sr²⁺ removal of KSbP₂O₈ mainly stems from ion exchange between Sr²⁺ and interlayer K⁺ in KSbP₂O₈, which is attributed to the synergy between the Sb⁵⁺-induced Brønsted acidity and the high charge density of the anionic framework. This study demonstrates the exceptional capability of phosphatoantimonates to selectively capture Sr²⁺ under acidic conditions, highlighting the potential of phosphatoantimonates as effective scavengers for radiostrontium remediation.</p>