Resin composition, resist underlayer film, resist underlayer film-forming method and pattern-forming method

A resin composition for forming a resist underlayer film, comprising:

• a resin that includes an aromatic ring;
• and
• a crosslinking agent having a partial structure represented by a following formula (i):
• wherein, in the formula (i),
• X represents an oxygen atom, a sulfur atom, *—COO— or —NRA—, wherein RA represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 30 carbon atoms, and * denotes a site bonded to R1;
• R2 represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 30 carbon atoms;
• R2 represents a hydroxy group, a sulfanil group, a cyano group, a nitro group, a monovalent hydrocarbon group having 1 to 30 carbon atoms, a monovalent oxyhydrocarbon group having 1 to 30 carbon atoms or a monovalent sulfanilhydrocarbon group having 1 to 30 carbon atoms;
• n1 is an integer of 1 to 12;
• n2 is an integer of 0 to 11, wherein a sum of n1 and n2 is an integer of no greater than 12, and in a case in which at least one of X, R1 and R2 is present in plural number, each of the plural Xs, the plural R1s and the plural R2s are a same or different;
• and
• p is an integer of 1 to 3.