In this study, the stability constants of a mixed ligand complex of lanthanum(III) ion by using ethylenediaminetetraacetic acid (EDTA, H(2)A) as a primary ligand and 2,3-dihydroxybenzoic acid (2,3-DHBA, H3B) as a secondary ligand have been investigated. The stability constants of the binary and mixed ligand complexes have been determined by using a potentiometric method and the BEST computer program at 25 degrees C, in a 0.1 M NaCl ionic medium. In addition, the identified ternary complex by potentiometry was isolated as a solid, and the structural characteristics have been examined using IR, NMR, elemental analysis, differential thermal analysis, thermogravimetric analysis, and the conductivity method.