Electrochemical deposition of Ag on a 23×√3 reconstructed surface of Au(111) electrode at various potentials was followed by scanning tunneling microscope (STM) in situ in real time. Ag was nucleated on the faulted hcp region of the reconstruction and grew preferentially along the hcp lines (the <11-2> directions), resulted in a line shape. Formation of the Ag lines with biatomic height was more favored than that with monatomic height at more negative potentials in the range of −0.2∼+0.3 V (vs. Ag/AgCl). The growth mode of the potentiostatic electrochemical deposition of Ag on the reconstructed Au(111) electrode surface observed here is quite different from those previously reported for the electrochemical deposition on Au(111)-(1×1) electrode and deposition under ultra-high vacuum (UHV) condition on the reconstructed Au(111) surface, showing the importance both of substrate surface structure and electrode potential.