Abstract: In present research, the effect of gamma radiation on the absorption and fluorescence spectra of laser organic dye (Rhodamine B) dye which have dissolved in ethanol at different concentrations were studied. The optical properties (absorption, transmittance, linear absorption index, linear refractive index and energy gap) were calculated as well as calculation the lifetime and quantum efficiency of the fluorescence. The results shows the increasing of absorption and fluorescence values after radiation due to decreasing of the energy gap.