Au-Ni alloys were electrodeposited from sulfate-based, weakly complexing electrolytes with various Ni concentrations. EQCM data show that by co-deposition with Au, Ni electrodeposition is strongly depolarized and deposition rate is greatly enhanced at a given potential. Composition analysis for alloy films confirms that Ni is incorporated into the alloys at potentials more positive than its own redox potential. A continuous shift of the alloy reflections (111) and (200) was observed by X-Ray Diffraction, which is consistent with the formation of a series of solid solutions, in stark contrast with the immiscibility expected by the thermodynamics of the bulk alloys. HR-TEM for alloy films of similar to 60% Ni shows a grain size of less than 15 nm of Au rich grains, and smaller (2-3 nm) Ni-rich grain boundaries with poor crystallinity. This unexpected configuration is probably originated by the attractive interaction of Au and Ni at the solid/electrolyte interface during growth, compensated over time by the strain energy originated by the difference in atomic volumes. The resulting nanoscale decomposition suggests the possibility to tailor atomic configuration and therefore properties via tailoring of the deposition parameters. (C) 2016 The Electrochemical Society. All rights reserved.