Distinct structures of the α-fucose branches in fucosylated chondroitin sulfates do not affect their anticoagulant activity. Fucosylated chondroitin sulfate (FCS) is a glycosaminoglycan found in sea cucumbers. It has a backbone like that of mammalian chondroitin sulfate (4-β-d-GlcA-1→3-β-d-GalNAc-1)n but substituted at the 3rd position of the β-d-glururonic acid residues with α-fucose branches. The structure of these branches varies among FCSs extracted from different species of sea cucumbers, as revealed by solution NMR spectroscopy. Some species (Isostichopus badionotus and Patalus mollis) contain branches formed by single α-fucose residues but with variable sulfation patterns (2,4-, 3,4- and 4-sulfation). FCS from Ludwigothurea grisea is distinguished because it contains preponderant branches formed by disaccharide units containing non-sulfated and 3-sulfated α-fucose units at the reducing and non-reducing ends, respectively. Despite the structural variability on their α-fucose branches, these FCSs have similar anticoagulant action on assays using purified reagents. They have serpin-dependent and serpin-independent effects. Pharmacological assays using experimental animals showed that the three types of FCSs have similar antithrombotic effect and bleeding tendency. They also activate factor XII on the same range of concentration. Based on these observations, we proposed that only few sulfated α-fucose branches along the FCS chain are enough to assure the binding of this glycosaminoglycan to proteins of the coagulation system. Substitution with additional sulfated α-fucose does not increase further the activity. Overall, the use of FCSs with marked variability on their branches of α-fucose allowed us to establish correlations between structures vs biological effects of these glycosaminoglycans on a more refined basis. It opens new avenues for therapeutic intervention using FCSs.