The stability constants of Cu (II), La (III) metal ions with substituted azoles has been studied by pH-metric technique at 0.1 M (KNO3) ionic strength at 27 ± 0.10C in aqueous medium. Also the effect of ionic strength on stability constants of chelates of azoles in 70% DMF-Water system with pH-metric technique has been studied. The data obtained was used to study the correct mechanism of complexation, to determine thermodynamic properties and to study proton-ligand and metal-ligand stability constants.