A glycosaminoglycan 6-O-sulfotransferase having an activity of transferring sulfate to a hydroxyl at position 6 of a glycosamine residue of a glycosaminoglycan, which has a ratio of relative activities to substrates satisfying completely desulfated N-acetylated (CDSNAc) heparin/completely desulfated N-resulfated (CDSNS) heparin .gtoreq.0.05 and a molecular weight as calculated from constituent amino acids of from 53,000 to 58,000 daltons.