Abstract: Crude dextran, a fermentation product of cane sugar with Leuconostoc mesenteroides No. 1226, is partially depolymerized to obtain clinical dextran (D), which has been used effectively as blood volume expander. It has been. reported that side effects in clinical use is attributed to undesirable structure of D.The structure of D is determined by permethylation using Hakomori′s procedure, followed by acid hydrolysis, sodium borohydride reduction and acetylation. The methylated and acetylated components are then separated by gas chromatography and identified by mass spectroscopy. The results show that D contains α-D-(1→6) linkages in the main chain, with branched points of α-D-(1→3)and a few α-D-(1→2) linkages. The molar ratio of glucosyl residues with different linkages is calculated by using molar effective carbon response, and the structure of D is primarily postulated with an average repeating unit of 12 sugar residues.