The unsolved problem of plastic waste utilization has led to a great interest in the development of studies of accelerated degradation of polymers. In this work the course of photo-oxidative degradation of some water soluble polymers such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA) and poly(vinylpyrrolidone) (PVP) in the presence of hydrogen peroxide has been investigated. The following methods have been applied: viscometry, IR and UV-Vis spectroscopy, gel permeation chromatography and chemical analysis. The hydrogen peroxide is an unstable compound which undergoes photolysis upon UV irradiation. Free radicals (HO9 and HO9 2 ) formed in this process are efficient initiators of polymer degradation. The changes of the viscosity and the average molecular weight indicate that the rate and efficiency of photodegradation of PAA, PMA and PVP in the presence of H 2 O 2 is much higher in comparison with respective values obtained in the absence of this agent. Spectroscopic data show that some simultaneous competitive processes (degradation, oxidation and chromophores formation) take place in UV irradiated polymers. In PAA photocrosslinking reaction occurred. The efficiency of this reaction was estimated by the amount of formed insoluble gel. Contrary to degradation, photocrosslinking of PAA was hampered by H 2 O 2 . It was found that photochemical reactions in polymers depend on the concentration of H 2 O 2 and dose of UV irradiation. The mechanisms of reactions occurring in the studied systems have been discussed. Moreover, the influence of the chemical structure of macromolecules on the course of photo-oxidative degradation has been considered. It has been also shown that acceleration of PVP photodegradation by H 2 O 2 is larger than that by FeCl 3 . Some additional data indicating the changes of physical properties of photodegraded polymers have been presented. It can be concluded that hydrogen peroxide may significantly accelerate the decay of water soluble polymers present in municipal sewers.