The photooxidative degradation of a polyether/aliphatic diisocyanate based polyurethane, ETHDI, was studied using FTi.r. spectroscopy. It was confirmed that the oxidation of this type of polyurethane results from the important sensitivity of the polyether soft segments to oxidative degradation. The photooxidation mechanism of the polyether segment was studied using the photodecomposition of polytetramethylene glycol, PTMG, as a model for that of the soft segments of ETHDI. The photooxidation of PTMG was studied until the ultimate degradation of the polymer and the different photoproducts were identified by analysis of both the solid polymeric matrix and the gas phase. Oxidation of the ether groups produced formates, which further decomposed to give ethylene and methyl formate, and regenerated the formates. For irradiation of the ETHDI polymer until the total disappearance of the ether groups, the decomposition of the urethane functions was observed and the corresponding photoproducts characterized.