Abstract: It was found that among 9 kinds of organic solvents tested,1,2-propanediol showed the most remarkable sensitization effect on the fluorescence intensity of the coordination complexes formed between iso-orotic acid and europium(Ⅲ),terbium(Ⅲ) or dysprosium(Ⅲ). Based on these phenomena,new methods for the fluorospectrophotometric determination of Eu(Ⅲ),Tb(Ⅲ) or Dy(Ⅲ) were proposed and the mechanism of the sensitization effect of the organic solvents was discussed. The fluorescence reaction of either of the 3 rare earth elements with iso-orotic acid was carried out in a solution of ammoniacal buffer (pH 8.0),containing 40% (by volume) of 1,2-propanediol and 7.0×10-4mol·L-1 iso-orotic acid,and the following results were obtained for Eu(Ⅲ),Tb(Ⅲ) and Dy(Ⅲ) respectively: wavelength of excitaction 300 nm,wavelength of emission 612,544,574 nm,range of linearity 0.60-8.00,0.000 5-3.00,0.20-7.00 mg·L-1,detection limits 0.56,5.3×10-4,0.18 mg·L-1. In the test for recovery by the standard addition method,values of recovery obtained were in the range of 95.6%-109.3%.