CePr and CeMn mixed oxide catalysts were synthesized by inserting Pr and Mn atoms into CeO2. Catalytic performance on soot combustion was investigated, and several characterizations were carried out using X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller surface area analysis, H-2 temperature-programmed reduction, and X-ray diffraction. Results show that a cubic fluorite structure solid solution can be formed with Pr and Mn doped into CeO2 lattice. Three oxygen species, namely, lattice oxygen O-I (O2-), defect oxygen species O-II (O-2(-), O-2(2-), and O-), and hydroxyl-like groups and adsorbed molecular water O-III, exist in the solid solution structure. In general, the defect oxygen species O-II is responsible for soot combustion. CePr exhibits fast oxidation rate because of the presence of open oxygen migration channel (O-I <-> O-II <-> O-III), and reactive oxygen species O-II can continue to be replenished. CeMn possesses a large amount of surface active oxygen, which results in excellent low-temperature catalytic activity.