We report the multistep electrolytic process for the synthesis of high T c single phase HgBa 2 Ca 2 Cu 3 O 8+δ (Hg-1223) superconducting films. The process includes : i) deposition of BaCaCu precursor alloy, ii) oxidation of BaCaCu films, iii) electrolytic intercalation of Hg in precursor BaCaCuO films and iv) electrochemical oxidation and annealing of Hg-intercalated BaCaCuO films to convert into Hg 1 Ba 2 Ca 2 Cu 3 O 8+δ (Hg-1223).Films were characterized by thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrolytic intercalation of Hg in BaCaCuO precursor is proved to be a novel alternative to high temperature-high pressure mercuration process. The films are single phase Hg-1223 with T c = 121.5 K and J c = 4.3 x 10 4 A/cm 2 .* The corresponding author