A resist underlayer film forming composition used in a lithography process includes: a polymer (A) containing a unit structure having a hydroxy group, a unit structure having a carboxy group, or combination thereof; a crosslinkable compound (B) having at least two vinyl ether groups; a photoacid generator (C); a C4-20 fluoroalkylcarboxylic acid or a salt of the fluoroalkylcarboxylic acid (D); and a solvent (E). The polymer (A) includes a unit structure selected from unit structures of Formula (1), Formula (2), and Formula (3);