Films of low-density polyethylene (LDPE) were exposed to artificial ageing in a photochemical reactor, and photochemical ageing was observed by tensile measurements. Oxidative degradation was characterized from carbonyl groups formation using infrared spectroscopy. Only ultimate properties seem to be affected, elastic properties being practically unaffected. In fact, the most obvious chemical effect induced in LDPE by exposure is the formation of carbonyl groups easily observable by infrared spectroscopy. Some elementary acts of the oxidation process induce chain scissions responsible for the decrease of elongation at break.