Selective reduction of supported CuO to Cu2O was realized using the strategy of vapor-induced reduction, in which HCHO/H2O vapor diffuses into the pores of the support and interacts with predispersed CuO. This new strategy allows the fabrication of supported cuprous sites at much lower temperatures within a short time, avoids the formation of Cu(0) with a Cu(I) yield of nearly 100%, and results in materials with good adsorption performance, which is impossible to achieve by conventional methods.