The present work investigates the fabrication of Au nanostructures using the masking effect of carbon patterns deposited by the electron-beam (E-beam) of a scanning electron microscope for electrochemical reactions. E-beam induced deposition is based on the decomposition of residual hydrocarbon species (molecules from the pump oil) to create a solid deposit at the point of impact of the E-beam. Subsequently, such E-beam deposited matter is used to completely block the electrochemical deposition of Au in the nanometer scale. In this work, several factors affecting the resolution of the process are studied. Electrochemical conditions as well as control of the E-beam C-deposit are investigated to optimize the lateral resolution of the process. Especially, it is demonstrated that the beam energy used for depositing the C-mask plays a crucial role in fabricating Au nanostructures in the sub-50 nm range. (C) 2004 The Electrochemical Society.