Glycopolymers carrying sulfated saccharides with modest sugar contents (11% and 28%) were found to suppress the formation of amyloid fibrils by amyloid beta peptides (A beta(1-42), A beta(1-40), and A beta(25-35)), as evaluated by thioflavin T assays and atomic force microscopy observation. Circular dichroism spectra showed that the conformation of amyloid beta peptides depended on the glycopolymer additives, and that the glycopolymer additives reduced the beta-sheet contents. Neutralization activity was confirmed by in vitro assay with HeLa cells. The sulfate group and the appropriate sugar contents were essential for the inhibitory effect.