Abstract: The determination of trace uranium in phosphoric acid and phosphate, solutions by means of the laser induced fluorescence method is investigated, with detailed study on the intensity and lifetime of uranium fluorescence in ortho-phosphoric acid, ortho-phos-. phate, meta-phosphate and pyro-phosphate media. Ortho-phosphoric acid enhances the fluorescence intensity more strongly than sulfuric acid or sulphate. The intensity of uranium fluorescence increases with an increase of phosphoric acid concentration, and a saturation value of intensity is reached when the concentration exceeds 1 M. The fluorescence intensity of uranium in phosphoric acid solu- tion can be enhanced with the addition of ammonium phosphate which is best suited for fluorescence enhancement.The detection limit of uranium is 0.02 ppb in 0.3 M H3PO4-1.0M NH4H2PO4 medium, and better than 0.01 ppb in 0.01 M Na4P2O7-pH 7.2 phosphate buffer medium.The lifetime of uranium fluorescence is 216 μs in orthophosphoric acid medium and about 50μs in ammonium phosphate or sodium pyro-phosphate medium. When the medium is fixed, the fluorescence intensity is directly propertional to the fluorescence lifetime.The effects of the interference of nineteen ions on the determination of uranium are measured, and it is found that most of the ions have no interference. However, Fe, Pb, Mn interfere moderately, whereas Ag interferes strongly.