Abstract Ce 0.6 Y 0.4 O 1.8 (40YCO) nanoparticle sol was synthesized via the hydrolysis of a Ce–Y–triethanolamine (TEA) complex derived from the reaction of hydrate cerium (III) nitrate (Ce(NO 3 ) 3 ·6H 2 O), yttrium nitrate (Y(NO 3 ) 3 ·6H 2 O) and TEA in alcohol solution at room temperature. The resultant sol possessed excellent UV shielding ability and high transparency in visible light region, and can be stable for one month. Transmission electron microscopy (TEM) showed a particle size distribution of 4.1 ± 0.7 nm for 40YCO. X-ray diffraction (XRD) as well as selected area electron diffraction (SAED) gave evidence that the as-synthesized nanoparticles were well crystalline. The formation of a solid solution was monitored by XRD and ICP-MS. Moreover, zeta potential measurement and infrared spectra were employed to study the YCO particles.