Abstract Polyphenolic substances synthesized by plants are generally involved in protection against UV radiation and the attack of pathogenic microorganisms. Resveratrol (3,5,4′-trihydroxystilbene, RSV) is synthesized in its <i>trans-form</i> (<i>trans</i>-RSV) in plants under stress conditions like infections or UV exposure and has attracted attention as an antioxidant agent. <i>Trans</i>-RSV was irradiated with both UV-A (λ_MAX = 365 nm) and UV-B (λ_MAX = 300 nm) radiation in aqueous and ethanolic solutions at room temperature. The reactions were followed by UV–Vis spectrophotometry, HPLC with UV and fluorescence detection, and UPLC coupled to mass spectrometry detection. In both solvents the irradiation caused the fast isomerization of <i>trans</i>-RSV to cis-RSV. In ethanolic solutions, a strong fluorescent compound, identified as resveratrone (RSVT) was detected independently on the irradiation wavelength. In aqueous solutions, RSVT was not detected in both irradiation conditions. However, in aqueous/ethanol mixtures the amount RSVT was found to be proportional to the amount of ethanol in the solution. Under UV-B irradiation, both in ethanolic or water solutions other products were detected. Our results demonstrated that RSV is photosensitive and its photochemistry depends on the solvent nature and on the irradiation wavelength.Facultad de Ciencias ExactasInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas