ABSTRACTDifferent structures of Cu2O nanoparticles (NPs) were synthesized by using poly(2-vinylpyridine) -b-poly(ethylene oxide) (P2VP-b-PEO) block copolymers as capping agent. The method involve the complextion of P2VP-b-PEO with Cu(NO3)2 and then reduction of Cu2+ to Cu2O by hydrazine hydrate. By adjusting the molar ratio of hydrazine hydrate to Cu2+ (MR), hollow spheres, solid spheres, cubes and octahedron can be fabricated. However, when Au NPs are used as seeds for Cu2O formation, Au-Cu2O core-shell NPs were obtained and the MR have little effect on the morphology of Cu2O nanostructures. The prepared Cu2O NPs with different structures may find applications in solar energy photovoltaics and photocatalysis.