In previous papers [1] , [2] , [3] the photo-oxidation of an epoxy resin (DGEBA) cross-linked with the hardener methyltetrahydrophthalic anhydride (MTHPA) was studied. The chemical evolution of the surface was analyzed by FT–IR spectrophotometry with attenuated total reflection (ATR) and by X-ray analysis [2] , [3] . The analyses confirmed the presence of a thin photo-oxidation layer at the surface of the material, which was predicted from measurement of the organic matrix's ablation [1] . Ablation is due to the loss of volatile photo-oxidation products. A photo-oxidation chamber was designed to trap and analyze these products. The chamber was put into an artificial photo-aging cell and linked to a GC–MS instrument. Photo-oxidation mechanisms were constructed from the data obtained. These mechanisms led to the ablation of the epoxy matrix.