Immobilized trypsin on the glutaraldehyde activated chitosan beads was employed to purify trypsin inhibitor from the tuberous roots of sweet potato by means of affinity chromatography. The optimum conditions for the preparation of immobilized trypsin were investigated, and a maximum trypsin activity of 10 unit/g-beads was achieved in this study. Fifty-six percent of the activity of the trypsin inhibitor in the crude extract of sweet potato could be recovered through affinity chromatography. Seven visible bands by SDS-PAGE were suspected to be trypsin inhibitors, and all of the molecular weights were more than 20kDa.