Abstract <p>Using photochemistry and luminescence analysis methods, it is shown that 4-methyl-1-sulfo-anthracene eliminates the sulfo group with an α-methylanthracene yield of ~70% upon irradiation with the light of a DRSh-1000 mercury-arc bulb-shaped lamp in a 47–65% perchloric acid medium. This elimination is a single-photon process involving the S¹ singlet level, which undergoes deactivation faster than the sulfo group undergoes elimination. The sulfo group is hydrolyzed under conditions of specific acid catalysis; at a high acidity of the medium (<i>H</i>₀ &lt; −2), the reaction occurs without affecting the <i>meso</i>-position of the anthracene ring. The quantum yields of the dissociated and nondissociated 4-methyl-1-sulfoanthracene species, the activation energies for photodesulfurization and luminescence quenching, the lifetime of the excited state of the molecule, and the constants of the kinetic equations are determined.</p>