UV irradiation of trans-resveratrol leads to its photochemical isomerization and electrocyclization, giving rise to different byproducts. Preliminary attempts to purify and characterize these products were in the majority of cases unsuccessful. In the present work, the resveratrol photoreaction products were analyzed by HPLC, and one of these compounds, 2,4,6-trihydroxyphenanthrene (THP), was purified and unambiguously identified. The structure of THP was unequivocally characterized for the first time by combined GC-MS, ESI-MS/MS, NMR, and FT-IR analyses.