Even though the ultimate mechanical properties of degraded polymers are widely reported in the literature, few papers dealt with the elastic properties of polymers after submitted to a degradation source. This topic is important to the understanding of the effects of degradation in polymer chemical and physical structure and also in the design of products where load bearing capability is a relevant requirement. The aim of this paper was to investigate and effects of photodegradation on the Young modulus of polypropylene. Several exposure conditions were applied in order to get a wide picture of this effect and hence to propose a reasonable mechanism for this influence. The elastic characteristics were discussed based on the variations in carbonyl index and in crystallinity during exposure and a new elastic property, named global compliance, was proposed. This article also analyses the influence of ultraviolet source on the photodegradation behaviour.