The interaction of Acid Red 1 (AR 1) with Zn(II) and Ni(II) ions in NH3/NH4Cl buffer solution (pH = 9.20) was investigated for the first time by square-wave and cyclic voltammetry techniques. The voltametric behaviours of the formed complexes were discussed. From the obtained results, their overall stability constants were calculated by using different equations, suitable to the property of the complexation process. The reduction of Ni(II)-AR 1 complex was shown at more positive potential (-0.768 V) than that (-0.910 V) of free Ni(II) in the absence of AR 1. The logarithm of overall stability constant (log beta(1:2)) and stoichiometry of the complexation of Ni(II) with AR 1 were determined to be 9.30 and 1:2 (metal:ligand), respectively. However, the composition of the Zn(II)-AR 1 complex is 1:1, and the logarithm of its stability constant (log beta(1:1)) was determined as 3.66 by the direct monitoring of the current of free zinc(II).