A facile two-step process was developed to synthesize hierarchical nanostructured CuO. First, copper acetate reacts with ethylene glycol to produce organocopper precursors with tunable morphologies; second, the organocopper precursors are calcinated to produce CuO structures which preserve the morphology of the precursors. The product consists of nanometer-sized CuO crystallites self-organized into micrometer-sized monoliths with tunable complex structures, including microplates, doughnut-like structures, and multilayer microspheres. The doughnut-like CuO structure possesses high removal capacity for As(III) and can be easily separated and recycled during water treatment processes.