Abstract: Under the condition of 0.04 mol/LH₂SO₄ medium at 80℃ oxalic acid has catalytic effect on the fluorescense quenching reaction of rhodamine B oxidized by K₂Cr₂₇. Tap water cooling was selected for quenching the reaction. The effect of various factors on catalytic determination of oxalic acid has been studied spectrophotofluorimetrically. Among the media ofH₂SO₄, HCl and H₃PO₄, oxalic acid inH₂SO₄ has the most catalytic activity. The value of log(Fb/Fc) is increasing with the increase of the concentration of K₂Cr₂₇ in the range of 0～1.0×10^-3 mol/L. The value of log(Fb/Fc) increases slowly when the concentration of K₂Cr₂₇ is more than 1.0×10^-3 mol/L. A concentration of 1.25×10^-3 mol/L K₂Cr₂₇ was chosen for use. Rhodamine B is the most sensitivity indicator among rhodamine B, rhodamine S and butylrhodamine B. The value of log(Fb/Fc) is maximum when the concentration of rhodamine B is at 4.0×10^-6 mol/L. The optimum reaction temperature is at 80℃ and the reaction time is 8 minutes. 23 kinds of co existence substances which effect on the catalytic spectrophotofluorimetric determination of 1 μg/mL oxalic acid have been studied. The results show that most common substances do not interfere to the determination. A new catalytic spectrophotfluorimetric method has been descrided for the determination of 0.03～3μg/mL oxalic acid. The method has been applied to the analysis of oxalic acid in urine sample with satisfactory results.