The fluorescence characteristics of the complex of piperine with cation in micellar system were studied.At the same time,the influence of experimental condition on the fluorescence intensity was also studied.The experiments indicated that piperine had very low fluorescence signal itself.But in pH 8.77 Na 2HPO₄-NaH₂PO₄ buffer solution,both Mn(Ⅱ) and cationic surfactant cetyltrimethylammonium bromide can enhance the fluorescence intensity and stability of piperine.Based on this,a sensitive method has been developed for the quantitative determination of piperine in Mn(Ⅱ)-piperine-cetyltrimethylammonium bromide ternary system.Under the optimum conditions,there is a linear relationship between the enhancement of fluorescence intensity and the concentration of Mn(Ⅱ).The optimal conditions are as follows:the concentration of Mn(Ⅱ) is 2.5×10^-4 mol·L^-1 and the concentration of cetyltrimethylammonium bromide is 5×10^-4 mol·L^-1 .The fluorescence intensity was determined by a 1 cm quartz cell with the excitation wavelength of 352 nm and the emission wavelength of 452 nm.The linear range of concentration of piperine was 2.02-10.1 μg·mL^-1 with the relative coefficient of 0.998 5 and the detection limit of 0.060 2 μg·mL^-1 .The relative standard deviation (RSD) was 1.10%.The proposed method has been successfully applied to the quantitative determination of piperine in the Mongolian medicine Piper longum L,and the recovery was within the range of 97.6%-102.0%.The results were very satisfactory.