Preparation of polymer peroxides with peracid type having thermo-responsive function was examined by using acrylic acid (AA)-grafted polyethylene film (thickness = 30 mu m), into which thermo-responsive component, poly(N-isopropylacrylamide (NIPAAm)), was introduced by two photografting methods. One is photografting of AA/NIPAAm binary monomers and the other is two-step photogafting, where AA is first photografted to the polyethylene film and then NIPAAm is introduced into the AA-grafted film by second-step photografting. The grafted film (one-step sample) prepared by the former method exhibited a higher thermo-responsive character than that (two-step sample) prepared by the latter method, where the grafted films swelled in water below and shrank above a lower critical solution temperature of poly(NIPAAm). The grafted films thus obtained were subjected to peroxidation with hydrogen peroxide in the presence of methanesulfonic acid. About 50% of the initial amount of peroxides on the AA-grafted sample disappeared after thermal decomposition at 25 degrees C and 40 degrees C for 60 min in aqueous medium. On the other hand, about 50% (25 degrees C) and 90% (40 degrees C) of peroxides on the one-step sample remained stable under the same conditions, resulting in an improved stability of the peroxides at higher temperature. However, the decomposition of the peroxides was markedly promoted by the irradiation with light of lambda > 300 nm at 40 degrees C. Almost all peroxides on the two-step sample disappeared while generating hydrogen peroxide in aqueous medium at 25 degrees C and 40 degrees C, showing a decomposition behavior different from those on the one-step sample.