Epoxidation of propylene into propylene oxide (PO) in the gas phase is a highly challenging reaction. Cu-based catalysts have been active for this reaction, but the state of Cu as an active species is still debatable. In this paper, we report the propylene epoxidation activity of solution combustion synthesized Cu/CeO₂ catalysts with the CO + O₂ mixture at low temperatures (50-100 °C) peaking at ∼80 °C. The highest PO yield was obtained with 20-25% Cu loading in CeO₂. In contrast, the reaction over the catalyst containing nonreducible support such as Cu/SiO₂ occurred above 170 °C. Detailed structural characterization indicated two types of Cu species such as Cu²⁺ partly (∼3%) dissolved in CeO₂ forming a Cu_xCe_1-xO_2-δ phase and the remaining amount formed highly dispersed CuO as a separate phase. Thus, the highest activity relates to the optimum presence of CuO along with Ce_1-xCu_xO_2-δ. The reducibility of the Cu species in two phases was significantly shifted toward lower temperatures, indicating strong electronic interaction between the two phases. The substituted Cu²⁺ was reduced first, and then, the bulk CuO reduction was initiated. In situ spectroscopic studies showed Cu⁺ formation from Cu²⁺ over Cu/CeO₂ catalysts even at room temperature unlike in CeO₂ or CuO + CeO₂ physical mixtures, indicating strong electronic interaction between Ce_1-xCu_xO_2-δ and CuO phases on CO adsorption in the Cu/CeO₂ catalyst. It is proposed that substituted Cu²⁺ along with Ce⁴⁺ is reduced easily, and then, Ce³⁺ promotes the reduction of the interfacial CuO phase that might donate active oxygen species for epoxidation reaction.