Application of a constant cathodic current to an electrode in an alkaline Cu(II) lactate solution results in oscillation of the electrode potential during the electrodeposition of copper/cuprous oxide layered nanostructures. The electrochemical quartz crystal microbalance (EQCM) is used for in situ phase analysis measurements of the nanoscale layers and the results are compared with bulk XRD measurements. The EQCM is also used to estimate the layer thicknesses and overall modulation wavelength of the nanostructures. We propose that Cu2U is deposited during the positive spikes in electrode potential, while a composite of Cu and Cu2U is deposited during the more negative plateau region of the oscillation. The modulation wavelength calculated from the EQCM is in good agreement with that observed with scanning electron microscopy. The EQCM is shown to be a useful tool for estimating layer thicknesses and phase compositions for layers that are too thin to be examined by other instrumental techniques.