A continuous fluorometric assay system based on melittin and a pyrene derivative 1 for trypsin and its inhibitor screening is successfully developed by taking advantage of the noncovalent-binding-induced pyrene excimer. The 1 melittin assembly and its disassembly after further addition of trypsin are confirmed by the fluorescence changes at 475 nm. Such a system can be applied to other proteases of melittin, and essentially, the concept based on the noncovalent-binding-induced continuous fluorometric assay can be extended to other biochemical analyses.