The inhibition by melanoidin of trypsin was investigated in a kinetic approach. Melanoidin was prepared by the Maillard reaction between D-glucose and glycine, and BANA was used as a substrate. The inhibition was found to follow a non-competitive mode with a Ki of 5.8% and to be exerted through an electrostatic interaction between melanoidin and trypsin. Approximately 20% of the activity of trypsin survived even at a greatly increased concentration of melanoidin. The inhibiting mechanism of melanoidin might be due to an allosteric effect, which was probably different from a proteinaceous inhibitor such as ovoinhibitor diminishing trypsin-activity completely. The melanoidin molecule was thought to trap a great number of trypsin molecules, binding them and reducing their activity.