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The processes of redox interconversion of Cu and Cu2O sol nanoparticles in the presence of poly(N-vinylpyrrolidone) are studied. Reduction processes are conducted in the presence of tert-butylamine borane, and oxidation processes are carried out using Cu2+ ions. The successive oxidation-reduction of copper-containing nanoparticles is performed successfully several times. Stable Cu and Cu2O sols are obtained during all reduction-oxidation steps. Initially, only isolated spherical nanoparticles are formed; their average diameter increases at each step from 6.5 to 10 nm. With increasing number of interconversions, the associates of nanoparticles with spherical symmetry are first observed and then wormlike nanostructures are registered. At the final steps, the associates of nanoparticles with toroidal symmetry are formed.