provided are a “ eutectic colloidal crystal ” which is an aggregate of plural kinds of colloidal crystals having different lattice constants , a solidified body of the eutectic colloidal crystal , and methods for producing them . the eutectic colloidal crystal of the present invention contains two or more kinds of colloidal crystals composed of substantially monodispersed colloidal particles having different particle sizes . this eutectic colloidal crystal is obtained by providing a colloidal dispersion of two or more kinds of colloidal particles having different particle sizes , and a polymer which will not substantially adsorb to the colloidal particles dissolved in a dispersion medium , and allowing the colloidal dispersion to stand .