Antibiotics have saved countless lives and continue to be the backbone for treating bacterial infections. β-Lactam antibiotics have been successfully introduced as antibacterial agents and still the most popular drugs for treating bacterial infections and as a result, the biological applications of these compounds and their complexes have attracted remarkable attention as they can used as anti-bacterial and anti-cancer agents. From this point, the interactions of metal ions (Cu(II), Co(II), Ni(II), Zn(II), Eu(III) and Tb(III) with amoxicillin(H2Ax)(Ax) and some selected amino acids(L-glycine(Gly),L-methionine(Met),L-asparagine(Asn),L-histidine(His) and DL-alanine(Ala) have been studied potentiometrically at 20 oC and ionic strength 0.1M KNO3 in aqueous medium. The dissociation constants and formation constants of ligands and their metal complexes were calculated from potentiometric data using Irriving-Rossotti method. The acid-base properties of ligands were investigated and discussed. It was found that complexes formed were of the type of (1100) and (1110). The mechanism of ternary complexes formed is association manner. It was found that amoxicillin acts as a primary ligand for the interaction of metal ions in the presence of glycine, alanine or histidine amino acids. On the other hand in the case of methionine or asparagine, amoxicillin acts as a secondary ligand. Stabilities of ternary complexes with respect to metal ions were as the following order: Zn(II)< Cu(II) > Ni(II) >Co(II) for transition metal ions and Eu(III) > Tb(III) for lanthanide metal ions. The concentration distribution curves of the binary and ternary complexes formed in the solution were evaluated as a function of pH using HYSS program.