Ceria nanoparticles with 4 and 7 atom-% manganese dopant were synthesized through a template-free solvothermal method. The structure of the samples was characterized by powder X-ray diffraction (XRD). Monodispersed nanospheres of average size 130 nm were observed in transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and field-emission scanning electron microscopy (FE-SEM) analyses. Manganese ions were introduced into the system and it is confirmed that the Mn species dissolve within the CeO2 lattice by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Furthermore, the as-obtained Mn-doped ceria nanoparticles revealed superior catalytic performance in CO oxidation in contrast with pure CeO2 prepared by the same route.