The reconstruction of Au(111) to (root3 x 23) structure after the reductive desorption of a self-assembled monolayer (SAM) composed of 2-mercaptoethanesulfonic acid (MESA) has been imaged by in situ scanning tunneling microscopy (STM) in a 0.5 mol dm(-3) KOH aqueous solution. The STM images dearly show that after the reductive desorption of MESA the Au(111) surface reconstructs to the (root3 x 23) structure. The reconstruction starts from the edge, spreads gradually, and covers the entire terraces of Au(111) on the time scale of several minutes. Pits of the gold substrate are formed especially at the boundaries between the unreconstructed and the reconstructed areas during the spread of the reconstruction.