A fluorine-free aqueous sol-gel technique was used to fabricate YBCO superconducting thin films. Acetic acid was added in order to modify the complexation process taking place between the metal cations and the organic chelating agents. The electrical resistance and the pH value were used as indicators of the quality of the precursors. When pH = 6.5, the precursor solution had the lowest resistance, implying a good ionization of the starting metal elements. By using the optimal precursor, the film was found to have very small sized particles after pyrolysis. Consequently, the annealed YBCO films are characterized by a sharp superconducting transition with a J(C) (77 K) of 0.25 MA/cm(2). (C) 2013 Published by Elsevier Ltd and Techna Group S.r.l.