Trypsin is a serine protease found in the digestive system of many vertebrates where it hydrolyzes proteins. Through trypsinisation, it cleaves peptides at the carboxyl side of arginine and lysine, unless they are followed by a proline.

Trypsin has an optimal operating pH of about 7.5-8.5 and optimal operating temperature of about 37°C. Unlike chymotrypsin, the activity of trypsin is not affected by the inhibitor tosyl phenylalanyl chloromethyl ketone (TPCK).