The present invention provides algin oligosaccharide, degree of polymerization 2-22 and its derived product, by aside+combination, mannuronic acid -- Isosorbide-5-Nitrae glycosidic bond is made such algin oligosaccharide. Derived product its reduction of position -1 terminal be carboxyl free radical can by oxidation obtain. The present invention also provides the manufacture of algin oligosaccharide and its derived product comprising and alginate solution in water reacts under high press condition in the reactor, and 100-120 degrees Celsius, pH2-6,2-6 hours, after completed reaction, pH value was adjusted to 7. As a result oligosaccharides is oxidized in the presence of oxidant, then produces oxidation product. Algin oligosaccharide and its derived product of the invention can be used for preventing the manufacture of the medicament of Alzheimers dementia.
