Composites are frequently uncovered to show superior catalytic performance at mild conditions for a variety of emerging applications in energy and environment, while identity of low-temperature active species and their role remains elusive. Herein, we took CeO₂-CuO as a prototypical composite to sequence the active species responsible for the superior catalytic performance of CO preferential oxidation at low-temperature. Through data analyses of structure, reducible ability, adsorption/desorption behaviors of oxygen species, and in situ spectroscopic features, highly dispersed CuO_x species are experimentally identified to be the active centers that dominate the catalytic performance as represented by a redox temperature below 150 °C. The methodology of elevating the concentration of active species is further demonstrated by increasing annealing temperature as well as by tuning the dispersion of CeO₂ and CuO components that controls Ce³⁺ content in composite. These findings may provide hints of creating highly concentrated active sites when designing advanced composites for low-temperature catalytic applications.