This study presents an in-depth spectrophotometric investigation of ternary complexes of the rare earth element erbium (Er³⁺) formed using primary ligands—EDTA, HEDTA, CYDTA, and EGTA—and secondary bidentate ligands—maltol, tiron, kojic acid, and α-picolinic acid. The enhanced absorbance observed in ternary complexes relative to their binary counterparts is attributed to hyperchromic effects. These effects are leveraged to determine stoichiometry, which was consistently found to be 1:1:1 across all systems. Conditional stability constants were calculated and corrected using the ligands’ pKₕ values. The stability trend observed was EDTA/HEDTA: α-picolinic acid > tiron > kojic acid > maltol, and CYDTA/EGTA: α-picolinic acid > kojic acid > tiron > maltol. The significant increase in molar extinction coefficients in mixed-ligand complexes demonstrates their analytical value for erbium microdetermination.