There is provided a resist underlayer film forming composition that is used in a lithography process for the production of semiconductor devices and that can be developed with an alkaline developer for photoresists, and a method of forming a photoresist pattern by using the resist underlayer film forming composition. The resist underlayer film forming composition used in a lithography process for a production of a semiconductor device comprising: an alkali-soluble resin (a); a polynuclear phenol (b); a compound (c) having at least two vinylether groups; and a photoacid generator (d). The alkali-soluble resin (a) may be a polymer containing a unit structure having a carboxyl group, and the polynuclear phenol (b) may be a compound having 2 to 30 phenolic hydroxyl groups in the molecule.