Glycine max is nowadays cultivated throughout many countries due to the wide use of its seeds. Soybean derivatives are among the food products most consumed worldwide. Proteins and polysaccharides are the main soybean constituents. Its flour consists of milled and defatted material, which has its major use in the food industry and for the production of isolated soy protein. From the flour we have now obtained, by aqueous extraction, a Type I arabinogalactan (AG) containing 6% galacturonic acid. ¹³C NMR and methylation analyses of AG revealed a complex structure with a (1®4)-linked b-Galp main chain, mainly with side chains having O-5, O-3,5, and O-2,5 substituted a-Araf, and 4-O-substituted Glcp units. The presence of 20% protein makes us suggest that AG could belong to the arabinogalactan-protein class of molecules. The residue of an aqueous extraction was submitted to aqueous 2% KOH extraction (2 h, x 3, at 100 °C), and the extract was treated with acetic acid to pH 5.0. The soluble fraction was submitted to freeze-thawing processes, which resulted in a precipitate (SAcP). GC-MS analysis of derived alditol acetates showed Rha, Fuc, Ara, Xyl, Gal, and uronic acids in a molar ratio of 3:3:25:5:36:28. Different from AG, another isolated arabinogalactan was previously characterized (SAcP), and contained only 6.5% protein and a higher content of uronic acid. We thus believe that AG and SAcP could be different arabinogalactans. The study of these polysaccharides is of large interest since arabinogalactans isolated from other sources have often been reported to be immunologically active.