A composition for flattening uneven substrates. The composition for flattening uneven substrates, which is applied on an organic pattern, includes a solvent and a polysiloxane including a hydrolysis condensate of a hydrolyzable silane, wherein the polysiloxane includes silanol groups in a proportion of 20 mol % or less with respect to Si atoms, and the weight-average molecular weight of the polysiloxane is 1,000-50,000.