Poly(ethyleneoxide) (PEO) composites with SWy-1 montmorillonite were prepared by mixing the polymer and the clay in aqueous colloidal solutions. Thin films of the composites were obtained by solvent evaporation and exposed to 254-nm UV-irradiation. The photodegradation was monitored by FTIR and the chain scission reaction was confirmed by measurement of average molecular weights using size exclusion chromatography. The rate of oxidation of pure PEO was much faster than that of the composites (SWy-1/PEO). The SWy-1 clay stabilizes the polymer against UV irradiation. This stabilization is due to two factors: on one side, the absorption of UV radiation by the clay, and on the other the scattering of the incident radiation by the particles; both contributing to minimize the degradation rate of the PEO present in the composites. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013