Abstract: In this reaserch, we have studied the effect of pH value of sodium fluorescein in ethanol solution on its characteristics of laser energy conversion efficiency, absorption spectra and fluorescence spectra. By studying the absorption spectra, we have verified the existence of various tautomers of sodium fluorescein in ethanol solution. Each tautomer with different concentration is in acid-base equilibria in the solution at various pH values. The absorption cross section, σ_p, for λ=337.1 nm and fluorescence quantum yield, φ, of each tautomer are quite different. When pH value increases, the concentration of dianion, which has the largest value of σ_p and φ in all tautomers, gradually increases in the solution. So that, the laser energy conversion efficiency of sodium fluorescein solution will enhance, as its pH value increases due to the dependence of the laser output energy of dye solution on the value of σ_p and φ.