Abstract: In an acetate buffer of pH 4.0,and heated in a water bath at 80 ℃,folic acid was oxidized by KMnO4 to give a product called 7-amino-3 carboxy-pyrazinopyrimidine,producing fluorescence with its intensity much higher than the fluorescence intensity of folic acid itself.It was found that linear relationship between the magnitude of fluorescence intensity of the reaction product and the concentration of folic acid was obtained in the range of 0-1.6 mg·L-1.Detection limit of this method was 51 μg·L-1.In its application to the analysis of milk powder,value of RSD′s (n=6) obtained was 2.52%.