The shape control of Au nanocrystals is crucial to their catalytic applications and optical properties. Well-defined Au nanodendrites (NDs) have been prepared on a glassy carbon electrode using low-potential synthesis, assisted by ethylenediamine (EDA). The effects of applied potential, deposition time, and HAuCl(4) (or EDA) concentrations on the morphology of the Au deposits are discussed in our work. The growth mechanism can be explained by a two-staged growth of dendrites: initial branching and subsequent dendritic growth. The Au NDs exhibits superior catalytic performance toward ethanol oxidation, in comparison with the polycrystalline Au nanoparticles. The simple and facile synthetic technique can be applied to the construction of other metals with complex hierarchical structures on a large-scale.