This article reports a study of the influence of UV light irradiation in the presence of oxygen on both the chemical structure evolution and mechanical properties of an acrylicmelamine (AM) thermoset. Photo-oxidation of the thermoset was investigated by several techniques, such as IR spectroscopy, DMA, headspace-SPME and atomic force microscopy (AFM). The measurements by infrared spectroscopy combined with gas analysis allowed us to elucidate details of the reaction mechanisms that are difficult to detect by only spectroscopic measurements. This approach was used to probe mechanistic aspects of the photo-oxidation of acrylic-melamine (AM) thermoset and was completed by dynamic-mechanical measurements combined with AFM and micro-hardness measurements, which revealed the effect of photo-oxidation on the mechanical properties of the thermoset.