Abstract: The object is to provide a screening method for evaluating a large number of candidate compounds with sufficient accuracy, which uses aligned spheroids having equal sizes. The object is achieved by a method for screening for a substance that acts on spheroid formation, which comprises the following steps: (1) the step of inoculating cells on a plate on which a plurality of wells are regularly arranged (well plate), wherein each of the wells has a lowly adsorptive bottom having a U-shaped section, at a density effective for formation of spheroid, and culturing the cells in the plurality of the wells; (2) the step of contacting the cells with a test substance; and (3) the step of observing whether the cells contacted with the test substance form a spheroid or not, and evaluating action of the test substance on spheroid formation on the basis of the observation result as an index.