Copper nanocrystals have been grown on thin polypyrrole films obtained by electropolymerization on a gold electrode from CuSO4 solution electrochemically in both potentiostatic (constant potential) and galvanostatic (constant current) modes. A variety of copper nanostructures including fractals, nanowires, and cubic nanocrystals have been observed in the galvanostatic mode, in contrast to a single predominant type of nanostructures obtained by manipulating the under-peak potential (fractals) or over-peak potential (cubic nanocrystals) in the potentiostatic mode. The homogeneous distribution of nanocrystals observed at over-peak potential is consistent with an instantaneous growth mechanism. Depth profiling by X-ray photoelectron spectroscopy further reveals the presence of an ultrathin copper oxide layer on the surface of these nanocrystals.