Abstract: AIM　To study the structural characterization of an acidic polysaccharide, H3, isolated from the seeds of Cuscuta chinensis Lam. METHODS　Both chemical (such as sugar component analysis, methylation analysis, reduction of uronic acid, partial acidic hydrolysis, etc.) and spectral analysis (¹HNMR, ¹³CNMR, IR, etc.) were used to investigate the structural characterization of H3. RESULTS　The molecular weight of H3 was estimated to be more than 1.0×10⁶. The analytical results of sugar components indicated that H3 composed of Rha, Ara, Gal, and Gal A. Methylation analysis, partial acidic hydrolysis and 1H, ¹³CNMR further identified the linkages and sequence of the residues of H3. CONCLUSION　These results suggest that H3 is a highly branched heteropolysaccharide with structure elucidation for the first time.