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The TiO₂-assisted photodegradation of anionic eosin has been examined in TiO₂ aqueous dispersions under illumination by visible light. Eosin is easily decomposed photochemically by visible light in the presence of TiO₂ particles. The degradation kinetics followed a Langmuir-Hinshelwood type equation. The rate was greater in acid media than in neutral and alkaline media, which correlates with the adsorption behavior of eosin on the TiO₂ surface. Adsorption of eosin is a prerequisite for the TiO₂-assisted photodegradation. The evolution of CO₂ occurred concomitantly with the photodegradation of eosin. A plausible mechanism of degradation is discussed.