A composition for forming a resist underlayer film includes: (A) a crosslinkable compound represented by formula (I) and (D) a solvent. [In the formula, n is an integer of 2-6, the n-number of Z each independently are monovalent organic groups including a mono-, di-, tri-, tetra-, penta-, or hexaformylaryl group, the n-number of A each independently represent OCH.sub.2CH(OH)CH.sub.2O or (BB), and T is an n-valent hydrocarbon group and/or repeating unit of a polymer optionally having at least one group selected from the group made of a hydroxy group, an epoxy group, an acyl group, an acetyl group, a benzoyl group, a carboxy group, a carbonyl group, an amino group, an imino group, a cyano group, an azo group, an azide group, a thiol group, a sulfo group, and an allyl group and optionally interrupted by a carbonyl group and/or an oxygen atom.]