There is provided a composition for forming an underlayer film used for an underlayer of a self-organizing film. An underlayer film-forming composition of a self-organizing film, the underlayer film-forming composition including a polymer made of a unit structure derived from an optionally substituted styrene and a unit structure derived from a crosslink forming group-containing compound, the polymer containing 60 mol % to 95 mol % of the unit structure derived from the styrene and 5 mol % to 40 mol % of the unit structure derived from the crosslink forming group-containing compound relative to the whole unit structures of the polymer. The crosslink forming group is a hydroxy group, an epoxy group, a protected hydroxy group, or a protected carboxy group. The crosslink forming group-containing compound is hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, hydroxystyrene, acrylic acid, methacrylic acid, glycidyl methacrylate, or glycidyl acrylate.