The interaction between monoamine oxidase(MAO)and substrate Kyn was characterized by affinity capillary electrophoresis.The specific interaction between them was further demonstrated by adding an inhibitor clorgiline to MAO.The results demonstrated that the relative migration time ratio(RMTR)of Kyn decreased with the increase of MAO concentration in running buffer and the chromatographic peak of Kyn migrated far from that of triethyl benzyl ammonium chloride(TEBA) gradually.However,after adding the MAO inhibitor clorgiline,it was found that the values of RMTR of Kyn increased.This showed that the active site of MAO was occupied by clorgiline and the interaction between Kyn and MAO was inhibited.The developed method can be used to characterize the specific interaction between MAO and Kyn.Compared with the traditional methods of MAO inhibitors screening,eg.spectrophotometric assay and radiochemical analysis,the presented method could provide a potential analytical tool for the screening of MAO inhibitor with the advantages of rapidness,convenience and less sample consumption.