A technique for efficiently sealing many substances, such as beads, nucleic acid, protein, virus, cells, and lipid membrane complex, into an array is provided.The present invention provides a method for sealing a substance, including: (i) a step of introducing a first solvent containing a substance on a substrate on which a plurality of receptacles capable of storing the substance are formed separated from each other by a side wall; and (ii) a step of introducing a second solvent having a greater specific gravity than that of the first solvent onto the first solvent, the step (ii) being carried out after the step (i).