Decay processes of multi-layered islands on Au(100) surfaces, as well as nano-holes on Au(100) and Ag(100) surfaces in sulfuric acid aqueous solution under potential control have been investigated by in-situ electrochemical atomic force microscopy (EC-AFM). The influences of surface excess charge and of the high electric field at metal/electrolyte interface on the decay processes have been discussed. The decay rate of the first layer of the multi-layered islands is constant independently of the time elapse, suggesting that the detachment of the atoms from the step edges is a limiting process for the decay. The decay rate of the second or the third layer after the complete collapse of the upper layer is almost the same as that of the first layer. The rate is much greater than that before the complete collapse of the upper layer. The decay rate of the nano-islands and -holes on Au(100) has a minimum near the zero charge potential, and increases as the potential varies from the minimum.