Abstract: In a borax-HCl buffer medium of pH 9.2 and in the presence of CTMAB, fluorescence quenching effect was observed when ellagic acid was reacted with Y(Ⅲ). Based on this fact, a method of fluorospectrophotometry for the determination of Y(Ⅲ) was proposed. The magnitude of decrease in fluorescence intensity (ΔIf) of the reaction solution were measured at the wavelength of 454 nm by taking the difference between emission fluorescence intensity of the blank solution and the sample solution. Linear relationship between values of ΔIf and concentration of Y(Ⅲ) was found in the range of 2.0×10-6-8.0×10-5mol·L-1, with detection limit (3S/N) of 2.63×10-7mol·L-1. Values of recovery found were in the range of 99.0%-99.5%. Machanism of the action system was studied by resonance scattering spectrometry and UV-visible spectrometry.