An object of the present invention is to provide achondroitin sulfate having a decreased molecular weight whichhas utilization as an inhibitor of peritoneal disorder causedby long-term use of a peritoneal dialysis fluid containingglucose or a polysaccharide thereof as an osmotic agent,utilization as an osmotic agent in a peritoneal dialysis fluid,and the like. The chondroitin sulfate having a decreasedmolecular weight of the present invention as a means forachieving the object is characterized by having a weightaverage molecular weight of from 1000 to 20000 and containinga constituent disaccharide unit represented by the followingstructural formula in an amount of from 65 % to 100 %(molarratio) of the total.- [4GlcA.beta.1-3GalNAc ( 6S) .beta.1] -(wherein G1cA represents a D-glucuronic acid residue； GalNAcrepresents an N-acetyl-D-galactosamine residue； .beta.1-3represents a .beta.1-3 glycosidic linkage； .beta.1-4 represents a .beta.1-4glycosidic linkage； and (6S) indicates that position 6 of themonosaccharide residue is sulfated)
