In this paper an investigation on photo-dissociation mechanism of ethanol solutions of coumarin C311 is presented. The experiments on the-dissociation have been performed by detecting the changes in the absorption, fluorescence, infrared and NMR spectra of dye laser medium before and after the photogradation. It is shown that the photo-dissociation products of ethanol under UV and flash-lamp irradiations are acids. As a result, the following UV laser induced photochemical reaction mechanism is proposed: In UV laser or flash-pumped dye laser, O2 insolvent molecules due to the energy transfer of a dye molecule at a higher excited triplet state T2, are excited resulting in a leuco compound of dye by oxidation.