The quantum yield of singlet oxygen production was investigated in dodecylammonium propionate reversed micellar solutions containing 1,3-diphenylisobenzofuran and fluo-rescein as photosensitizer. The quantum yield was highly enhanced by the binding of fluorescein to reversed micelles, and increased with decreasing the solubilized water content in reversed micelles. Results obtained was discussed with the optical properties of fluorescein (absorption, fluorescence and phosphorescence) in reversed micellar solutions.