A copper film grew electrochemically at the interface between n-heptane and CuSO4 aqueous electrolyte, and its structure was investigated microscopically by using a scanning electron microscope, atomic force microscopy, X-ray diffraction, and transmission electron microscopy. The copper film electrodeposited at the interface had a bilayered structure: a very thin layer along the interface and a bunch of aggregates from the thin layer downward to the electrolyte bulk. The organic-liquid-side layer of the film of < 1 mu m in thickness was a polycrystalline composed of very fine particles of similar to 50 nm diam. The fine particles lined up in the growing direction, and each particle had no specific crystal orientation. Optical microscopic in situ observations during the growth of a copper film revealed that the thin layer grows preferentially along the interface and then the aggregates nucleate on the electrolyte side of the thin layer and grows downward to the electrolyte bulk. (c) 2007 The Electrochemical Society.