The optical anisotropy and intrinsic viscosity of DNA-Fe³⁺ complexes have been investigated. It was shown that the binding of iron ions to DNA causes the shrinkage of the macromolecule. The formation of such complexes is accompanied by increasing DNA optical anisotropy. We suggest that the binding of iron ions to widely spaced along the chain DNA groups creates the conditions for initiation of mutually oriented DNA fragments, thus, ensuring a higher molecular optical anisotropy.