Department of Chemical Technology, University Colleges of Science & Technology, University of Calcutta, 92 A. P. C. Road, Calcutta-700 009 The spectral properties and the photochemical reactions of anthraquinone in ethanol, aqueous ethanol. formic acid, sulphuric acid, sulphuric acid-ethanol and formic acid have been studied. In ethanol, aqueous ethanol and formic acid, the lowest excited state of the quinone is n—π* and the only photochemical reaction that can be detected is photoreduction to semiquinone while in concentrated (98%) to aqueous 60% H2SO4 as well as ethanol-H2SO4, the lowest state has more π —π* character and the sole photochemical reaction is photo-substitution to produce hydroxyanthraquinone.