Mesoporous nanosized powders with single-phase solid solution fluorite structure in the ternary oxide zirconia-yttria-titania system, with titania contents from 0 to 30 mol %, were synthesized by the selfassembling method associated with hydrothermal treatment using cetyltrimethylammonium bromide (CTAB) as the surfactant-directing agent and pore-forming agent. The resulting materials were characterized by X-ray diffraction (XRD), Raman spectroscopy (Raman), scanning and transmission electron microscopy (SEM and TEM), thermogravimetric analysis (TG-DTG), N2 adsorption/desorption isotherms (BET), and X-ray photoelectron spectroscopy (XPS). The as-synthesized mesoporous nanoparticles are single-phase crystallites with a crystal size and diameter between 6 and 12 nm and mean pore size around 2 nm. The specific surface area of the as-synthesized mesoporous samples after calcination at 550 °C remains as high as 140 m2/g. All spectroscopic methods clearly confirm the homogeneous incorporation of Ti4+ in the lattice of the nanocrystallites, forming a single-phase solid solution with fluorite structure and modifying the absorption spectra of the nanocrystallites. The mesoporous solid solution nanoparticles show significant activity in catalytic oxidation of methane in the range 650-750 °C.