There is provided a composition for forming a resist underlayer film that has a high selectivity of dry etching rate even though the composition contains an aromatic ring such as a benzene ring, and that is useful in lowering LER that presents a large problem in EUV (wavelength 13.5 nm) lithography. Moreover, another object is to obtain a composition for forming a resist underlayer film that provides a resist pattern having a desired shape on the resist underlayer film. A resist underlayer film forming composition for lithography which includes a polymer and a solvent, wherein in the polymer, diphenyl sulfone or a derivative thereof is introduced in the main chain of the polymer through an ether bond.