There is disclosed a resist underlayer film composition of a multilayer resist film used in lithography including (A) a fullerene derivative having a carboxyl group protected by a thermally labile group and (B) an organic solvent. There can be a resist underlayer film composition of a multilayer resist film used in lithography for forming a resist underlayer in which generation of wiggling in substrate etching can be highly suppressed and the poisoning problem in forming an upper layer pattern using a chemically amplified resist can be avoided, a process for forming the resist underlayer film, a patterning process and a fullerene derivative.