The photochemical behaviour of poly(vinylmethylether) (PVME) has been studied under irradiation at long wavelengths (λ ≥ 300 nm), at 60 °C and in presence of oxygen. In order to identify the photoproducts, the photooxidised samples have be submitted to chemical treatments and to photolysis (in the absence of oxygen). The results of the thermooxidation, at 80 °C, of PVME samples are also reported and compared to photooxidation results. The oxidation kinetic curves were plotted and the nature of the photoproducts as a function of irradiation time was analysed. The FTIR analysis of the oxidation was completed by the analysis of the whole photoproducts by mass spectrometry. A mechanism accounting for the main routes of oxidation is proposed.