In recent years, the hot water floor heating system has been popular instead of traditional or typical heating system such as air conditioner, oil stove, and electric carpet from the viewpoint of environmental problems in Japan. Plastic pipes such as PE-RT, cross-linked poly-ethylene (PEX) pipe, and polybutene (PB) are used as pipes of the system because of having the high temperature resistance materials. PE-RT is also well known to have a unique molecular structure and crystalline microstructure, which provides excellent long-term hydrostatic strength at high temperatures due to tie molecule entanglement without cross-linking polyethylene chain. In addition, it is known that plastics materials such as PE, polypropylene (PP), and PB are often degraded by contacting with metals such as Cu or Fe in water or in the ground. Therefore, it is important to investigate the influence of metal ion for plastics. However, there is a little basic research about the durability and degradation mechanism of PE-RT pipes, i.e. the oxidation mechanism of PE-RT pipes in the presence of active ion such as Cu or Fe. In this study, we try to evaluate the oxidization and mechanical properties by the acceleration degradation test in the presence of the copper ion. The difference of mechanical and chemical properties of these specimens was discussed on the basis of results of the tensile test, CL spectrometer measurement, SEM observation, and energy dispersive X-ray spectrometry (SEM-EDS) measurement, Raman spectroscopy. As results, the amount of O and Cu elements in the specimen after the hot water immersion test for 3000 h were increased with increasing the hot water temperature .Accordingly, it is considered that these specimens were oxidized by the catalytic effect of copper ion.