Inter α trypsin inhibitor (ITI) is a kind of protein widely existed in human and animal blood. ITI was composed of three peptides convalently linked together by a chondroitin sulfate chain. Two of the three peptides were linked to the chondroitin sulfate chain each by an ester bond between the carboxyl group of the final amino acid of the peptide and an internal C-6 hydroxyl group of the sugar chain. In extracellular matrix, this kind of ester bond can be transferred from chondroitin sulfate chain to hyaluronan. Thus the extracellular matrix and cell functions were regulated. The other peptide chain of ITI has kunitz type protease inhibitor domains. As a medicine, it can be separated from urine.