A method of preventing inter-foodstuff migration of water and a coloring matter in combining more than two foodstuffs is provided, wherein, in preparation of foods obtainable by direct combination of more than one foodstuff at least including one foodstuff containing either or both of water and the coloring matter, a water/coloring matter migration-proof agent in the form of sol or gel consisting of thickening polysaccharide or a mixture of thickening polysaccharide, oils-and-fats, and water-insoluble food fibers is interposed between one foodstuff containing the water or the coloring matter and the other contacting the one foodstuff. The thickening polysaccharide may be arum root or glucomannan in the form of sol or dissolved-in-water of refined flour or pasted glucomannan. The water/coloring matter migration-proof agent may be a mixture of a coagulating agent and a substrate consisting of arum root or glucomannan in the form of powder, sol or dissolved-in-water, or pasted glucomannan.