Scandium isotopes (44Sc, 47Sc) are more available and their properties are convenient for either PET imaging or radiotherapy. To use them in nuclear medicine, ligands forming complexes with a high stability are necessary. Available experimental data on stability constants for complexes of ligands such as EDTA, DTPA, DOTA, NOTA and TETA with various metal ions have been published. But scandium is the exception since scarce data is available in the literature. Values of stability constants of Sc(III) with the ligands were determined by free-ion selective radiotracer extraction, complemented by 45Sc NMR and potentiometry data. The thermodynamic stability of the Sc-complexes increases in the order TETA < NOTA < EDTA < DTPA < DOTA. The in vitro stability of the Sc(III) complexes was studied in the presence of hydroxyapatite and rat serum to estimate their in vivo stability. The most stable complex was shown to be Sc-DOTA.