In this work, acoustic emission was used to investigate the effects of ultraviolet radiation on the mechanical behavior of blends of polypropylene (PP) with ethylene-octene copolymer (EOC) containing photo stabilizers. Together with traditional techniques, like infrared spectroscopy and microscopy, the data obtained from acoustic emission helped the understanding of the failure caused by photodegradation and the influence of the stabilizing additives. Parameters like number and intensity of hits, released energy and acoustic events were recorded and related to the estate of the degradation and to the stress-strain behavior. The results confirmed the high sensitivity of PP/EOC blends to ultraviolet and the better performance of stabilized compounds, especially when hindered amine light stabilizers (HALS) were present. Acoustic emission experiments showed that in stabilized samples the crack propagation took place over a larger time interval, releasing more energy during failure and, hence, postponing the final fracture, from a few seconds for the neat blend to more than 500 seconds for the samples with 0.5% HALS.