Dextrans are polysaccharides with molecular weights ≥1,000 Dalton, with a linear backbone of α-linked D-glucopyranosyl repeating units. Dextrans are found as bacterial extracellular polysaccharides. They are synthesized from sucrose by Leuconostoc mesenteroides. Bacteria employ dextran in biofilm formation or as a protective coating to evade host phagocytes in the case of pathogenic bacteria.

Dextrans are used in many applications as platelet aggregants, plasma volume extenders, osmotic pressure regulators, stabilizers, organ separation media, matrix components, copolymers, microcarriers, binding agents, viscosity modifiers, antithrombotics, lubricants, and physical structure components.Dextran from Leuconostoc mesenteroides (Mw: 670,000) may be used as an analytical standard to calibrate the column for gel permeation chromatography (GPC). It has been used to sediment erythrocytes from blood along with 0.9% sodium chloride.

Use of dextrans as long and hydrophilic spacer arms to improve the performance of immobilized proteins acting on macromolecules.