The photoreaction of the antioxidant ellagic acid (EA) elicits a drastic coloration in solution from colorless to yellow in aerated tetrahydrofuran, which appears as a new absorption band at 405 nm. Analysis of the X-ray crystal structure suggests that the photo-oxidation product of EA is a multiple cleavage π-structure (Ox-EA) that results from the interaction of EA with singlet oxygen followed by sequential cleavage and rearrangement steps.