Disclosed is a composition for forming a base film for lithography, which enables a base film for lithography to have excellent optical characteristics and excellent etching resistance. Also disclosed are a base film made from such a composition and having high refractive index (n), low extinction coefficient (k), adequate transparency, high etching resistance and an extremely small sublimation content, and a pattern-forming method using such a base film. The composition for forming a base film contains an organic solvent and a naphthalene formaldehyde polymer having a specific unit, which isobtained by reacting at least naphthalene and/or an alkylnaphthalene with formaldehyde.