Abstract <p>Pyrazole-derived Schiff bases are mostly designed for the optical sensing of ionic species. In this research, a pyrazole-based Schiff base, 4-(4-methoxybenzylideneamino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (<b>MBz-AAP</b>), has been studied for its optical sensing properties towards various ionic species, including heavy metal ions and anions. Among these species, this probe exhibits a color change from colorless to maroonish-red for Fe²⁺ and Cu²⁺ ions, and colorless to yellow for <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\text{HSO}}_{4}^{ - }\)</EquationSource> <!--AnChem2560072Junaid-m1--> </InlineEquation> ions. These optical changes are found to be consistent with red shifts in the ultraviolet-visible absorption spectrum of MBz-AAP from 334 to 504, 510, and 387 nm for Fe²⁺, Cu²⁺, and HSO₄^– ions, respectively. Limits of detection (<b>LOD</b>) of MBz-AAP for Fe²⁺, Cu²⁺, and <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\({\text{HSO}}_{4}^{ - }\)</EquationSource> <!--AnChem2560072Junaid-m2--> </InlineEquation> ions are calculated to be 2.45, 3.34, and 2.24 μM, respectively. These LODs for Fe²⁺ and Cu²⁺ are much lower than their allowable limits in drinking water, i.e., 5.36 and 31.5 μM, respectively. Moreover, the stoichiometric binding ratios of Fe²⁺, Cu²⁺, and <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\({\text{HSO}}_{4}^{ - }\)</EquationSource> <!--AnChem2560072Junaid-m3--> </InlineEquation> with MBz-AAP are determined to be 1 : 1, with binding constants of 5.0 × 10³, 1.6 × 10³, and 7.05 × 10³ M^–1, respectively.</p>