There is provided a resist underlayer film having both heat resistance and etching selectivity. A composition for forming a resist underlayer film for lithography, comprising a reaction product (C) of an alicyclic epoxy polymer (A) with a condensed-ring aromatic carboxylic acid and monocyclic aromatic carboxylic acid (B). The alicyclic epoxy polymer (A) may include a repeating structural unit of Formula (1): (T is a repeating unit structure containing an alicyclic ring in the polymer main chain; and E is an epoxy group or an organic group containing an epoxy group). The condensed-ring aromatic carboxylic acid and monocyclic aromatic carboxylic acid (B) may include a condensed-ring aromatic carboxylic acid (B1) and a monocyclic aromatic carboxylic acid (B2) in a molar ratio of B1:B2=3:7 to 7:3. The condensed-ring aromatic carboxylic acid (B1) may be 9-anthracenecarboxylic acid and the monocyclic aromatic carboxylic acid (B2) may be benzoic acid.