In this work, we report an alternative assay for the determination of the inhibitory eVect on monoamine oxidase B (MAO-B) activity of probe compounds. Enzyme MAO-B exhibits Xuorescence emissions when it is excited at 412 nm. Using an inexpensive blue LED-like excitation source, we measured the quenching of Xuorescence intensity of MAO-B enzyme during the reaction with inhibitors. The applicability of the procedure is demonstrated by assays with L-deprenyl and berberine as inhibitors through the use of Xuorescence studies. The IC50 values of L-deprenyl and berberine were 0.04 and 90 M, respectively. The KI values were 0.020 and 47 M for L-deprenyl and berberine, respectively. These IC50 and KI values were similar to the values obtained with a standard method. These results demonstrate the feasibility of this method as an alternative to follow the inhibitory eVect on MAO-B.