Nano CeO2 colloids was prepared at the room temperature with cerium nitrate as cerium source, ammonia as pH regulator and polyvinyl alcohol as dispersant. The structure and properties of nano CeO2 colloids was characterized by FTIR, DLS, XRD and TEM. The possible formation mechanism and stable existence of nano CeO2 colloids was also be discussed. The results show that nano CeO2 colloids effectively dispersed in polyvinyl alcohol was obtained by mild and simple preparation process. Its crystal form was face centered cubic crystal system, the crystal structure was fluorite-type, the average diameter was about 28.2 nm, the storage time was 12 months. The UV aging resistance and thermal stability of nano CeO2 modified waterborne polyurethane (CWPU) and 2,4-dihydroxybenzophenone (UV-0) modified waterborne polyurethane (DWPU) were compared. The results of UV aging resistance showed that under the same test conditions, the ΔE, the b value and the wear loss compared with DWPU film decreased by 58.2%, 62.5% and 56.3% respectively, and the reduction rates of tensile strength and elongation at break were 47.8% and 43.3% of DWPU film respectively. The thermal stability test results showed that when the weight loss rate of DWPU film was 50%, the decomposition temperature was 310.62 ℃. At this temperature, the weight loss rate of CWPU film was only 12.35%. The temperature corresponding to the maximum thermal decomposition rate of CWPU film was 80 ℃ higher than that of DWPU film.