CuO with different nano-architectures was synthesized by spontaneous corrosion of copper in alkaline aqueous solutions without any additives. CuO nanoflakes were obtained by simply immersing a copper foil in NaOH solution, while flower-like architectures constructed with nanopetals were produced in Na2CO3 solution, indicating the pH value and the anions have a significant impact on the morphology and structure of CuO. The growth rate slowed down with the decrease of the alkalinity of the solution. In a more concentrated NaOH solution (1 M), polyhedron-like Cu2O was observed at the early stage before transforming into CuO nanoflakes. Based on these findings, massive production of nano-structured CuO powders was successfully realized by using copper powder as the precursor. The growing mechanism of flower-like CuO could be explained by the oriented attachment. The extensive sources of feedstock, the simple synthetic method and the uniform architecture of the products enable CuO to be utilized in a large scale.