New mixtures (A) of heparin-derived sulfated polysaccharides have average molecular weight 1500-3000, anti-Xa activity 120-200 IU/mg, anti-IIa activity 0-10 IU/mg and ratio of anti-Xa to anti-IIa activity more than 30； comprise 2-26 saccharide units； have a 4,5- unsaturated uronic acid 2-O-sulfate unit at one terminal； contain a specific hexasaccharide moiety designated DELTAIIa-IIs-Is hexasaccharide； and are in alkali(ne earth) metal salt form. New mixtures (A) of sulfated polysaccharides have the general structure of the constitutive polysaccharides of heparin, an average molecular weight of 1500-3000, an anti-Xa activity of 120-200 IU/mg, an anti-IIa activity of 0-10 IU/mg and a ratio of anti-Xa to anti-IIa activity of more than 30. The constitutive oligosaccharides of (A) comprise 2-26 saccharide units； have a 4,5- unsaturated uronic acid 2-O-sulfate unit at one terminal； contain a hexasaccharide moiety of formula (I) (designated DELTAIIa-IIs-Is hexasaccharide) and are in alkali(ne earth) metal salt form. An Independent claim is included for the preparation of (A).
