Abstract: To investigate the modulating effect of polysaccharide upon the mineralization of iron hydroxide, a series of simulative biomineralization experiments using dextran and chitosan as organic substrates were conducted in this paper. The results showed that iron hydroxide gel nucleated and grew in polysaccharide molecule, and the nanometric size akaganeite formed with the self-assembly effect of dextran or chitosan. The shape, size and crystal structure of the iron oxyhydroxide mineral formed from iron hydroxide gel depend on the type of polysaccharide and its concentration.