Atomic force microscopy (AFM) has been applied to investigate in situ the Hg/Au amalgam process by depositing the excess Hg atoms on an An electrode surface in an acidic solution, which has led to form an Au/Hg alloy layer. We found that the formation of alloy layer proceeded through an island-growth mechanism and the growth of these islands is always fed by dissolution of nearby gold clusters. Based on AFM observations, a simple model of the Hg/Au amalgam process is proposed.