Polyethylene glycol (PEG) photodegradation was studied in water under UV irradiation in the presence of catalytic amount of -TiO2 using hexaethylene glycol as a model compound. Full conversion was achieved in 7 h with an average quantum yield around 1%. Formic acid was found to be the main intermediate and was slower to oxidize into -CO2 (traces remains after 24 h). The other intermediates [ lower PEG, oxidized PEG (formates, aldehydes and acids, acetic acid)] of the photodegradation have also been identified and quantified. A mechanism based on previous literature but also taking into account these new observations is proposed.