Enhydra fluctuans leaves are traditionally sold on Indian markets for various health benefits. However, no phytochemical study on its high molecular weight compound has so far been performed. Chemical, chromatographic, ESI-TOF-MS, and NMR analyses of the water extracted carbohydrate polymer (CP) of E. fluctuans leaves showed the presence of a 24 kDa arabinogalactan having a (1,3)-linked beta-D-Galp main chain, substituted at O-6 by (1,6)-linked beta-D-Galp side chains. The latter residues were substituted at O-3 by (1,3)-, (1,5)-, and (1,3,5)-linked alpha-L-Araf chains, and nonreducing end-units of alpha-L-Araf and beta-D-Galp. This polymer contained esterified phenolic acids. Biochemical analysis revealed similarity in antioxidative potential between the identified carbohydrate polymer and known standard antioxidants. The highly branched side chains and the phenolic acid residues of the arabinogalactan might be the functional sites. Fluorimetric and ultraviolet spectrometric analyses showed that the studied carbohydrate polymer can form complex with bovine serum albumin having binding constant K = 2.42 x 10(6)/M and changes its microenvironment. Thus, traditional aqueous extraction method provides a carbohydrate polymer, which stimulates a fair biological response: this could represent an interesting approach in phytotherapeutic treatments.