Photo-oxidative degradation of poly(ethylene oxide) with small amount (1 and 3 wt.%) of cobalt (II) chloride was studied in acetonitrile solutions and in solid state. On the basis of FTIR, UV-Vis spectroscopy, GPC and viscometry measurements it was found that cobalt salt accelerates photodecomposition of PEG. DSC was applied for study of crystallinity changes in PEO and PEO + CoCl2 during UV-irradiation. The structure of PEO + CoCl2, mechanism of photoreactions and the influence of physical factors are discussed.