The polarographic behaviour of antimony(Ⅲ) complex with ethylenediaminetetraacetic acid (EDTA), including the calculation of stability constants, thermodynamic functions, and the mechanism of the complex formation, has not yet been studied in detail.In acidic 4 M sodium chloride solution, there is one cathodic diffusion wave corresponding to three electrons reversible electrode reaction of antimony(Ⅲ) at about -0.132 V (vs.S.C.E.) and pH 1.63.If to a strongly acidic solution EDTA is added even in high concentration, it exerts practically no influence on this wave.But if it is added to weakly acidic solutions (e.g.pH>2), there appears another wave which corresponds to the three electrons electrode reaction as before but at more negative potentials (e.g.at about -0.55 V at pH 2).If either the pH or the concentration of EDTA is reduced, the height of the second (more negative) wave decreases, while the first one appears again.The sum of both waves is constant and is independent of the concentration of EDTA and the pH value.