The structure of an amylopectin-iodine coloured complex has been investigated by small-angle X-ray scattering. The amylopectin shows the scattering profile of a branched polymer with persistent chain and curvature. The complexation of amylopectin with iodine induces different structural changes compared with those found for linear polymers, such as amylose and partially formalized poly(vinyl alcohol). This suggests that the presence of branch points in the amylopectin molecule contribute to steric hindrance in suppressing the structural change induced by the formation of polyiodine in the polymer chains.