The enzymatic activity of leucine aminopeptidase (EC 3.4.11.1) from the intestinal tract of sugarcane giant borer (Telchin licus licus) was assayed by using a simple and sensitive spectrophotometric assay that uses L-leucyl-2- naphthylamide as substrate. In this assay, L-leucyl-2-naphthylamide is hydrolyzed to produce 2-naphthylamine and Lleucine. The product 2-naphthylamine reacts with Fast Black K and can be monitored using a continuous spectrophotometric measurement at 590 nm. The data on the kinetic parameters indicates that the Km for the L-leucyl-2- naphthylamide at pH 7.0 was found to be lower than those found for other LAP substrates. The Km and Vmax for the LAP were determined to be 84.03 µM and 357.14 enzymatic units mg(-1), respectively. A noticeable difference of LAP activity between the two insect orders tested was observed. This method could be used to screen for natural LAP inhibitors.