We report a simple approach for the fabrication of cuprous oxide (Cu2O) nanocages and nanoframes possessing an unusual truncated rhombic dodecahedral, structure. An aqueous solution containing CuCl2, sodium dodecyl sulfate (SDS) surfactant, NH2OH center dot HCl reductant, HCl, and NaOH was prepared, with the reagents introduced in the order listed. Rapid seed-particle aggregation and surface reconstruction of the intermediate structure resulted in the growth of type-I nanoframes, which have only {110} skeleton faces and empty {100} faces, 45 min after mixing the reagents. Continued crystal growth for additional 75 min produced nanocages with filled {100} faces. The nanocages have diameters of 350-400 nm, and their walls are thicker than those of the nanoframes. Selective acidic etching over the {110} faces of the nanocages by HCl via the addition of ethanol followed by sonication of the solution led to the formation of type-II nanoframes, which have elliptical pores on the {110} faces. The morphologies of these nanoframes were carefully examined by electron microscopy. Without addition of ethanol, random etching of the nanocages can occur at a slow rate. Octahedral gold nanocrystals and high-aspect-ratio gold nanorods were successfully encapsulated in the interiors of these Cu2O nanocages by adding the gold nanostructures into the reaction solution. The formation process for such core-cage composite structures was studied. These composite materials should display interesting properties and functions.