In the present work, ZnO nanostructures with tunable size were successfully synthesized on non-seeded Cu substrates by a simple electrodeposition method. The effects of growth conditions on the morphology of the products were studied in detail by scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The as-prepared products exhibited flake-like morphology when the concentration of ZnCl2 was higher enough, while the products showed flower-like morphology when the concentration was lower enough. Field emission investigation indicated that the nanoflowers exhibited good emission properties. The ZnO nanoflowers show potential application as field emitters.