[en] The complex formation between vanadyl ions and ethylenedithiodiacetic acid (H₂L) has been studied at 25⁰C in 0.5 M-NaClO₄ as inert medium, by measuring the hydrogen ion concentration with a glass electrode. In acidic medium and in the investigated concentration ranges (2.07 mM<=Csub(M)<=7.50 mM, Csub(L) up to 12.5 mM)sup(*) the emf data can be explained assuming the equilibrium: VO²⁺ + L^2- reversible VOL logβ ₁₀₁ = 2.68 +-0.03. (author)