The present invention provides a resist underlayer film-forming composition for lithography for forming a resist underlayer film that can be used as a hard mask with use of hydrolysis-condensation product of a hydrolyzable silane which also absorbs KrF laser. A resist underlayer film-forming composition for lithography comprising, as a silane, a hydrolyzable silane, a hydrolysis product thereof, or a hydrolysis-condensation product thereof, wherein the hydrolyzable silane includes a hydrolyzable silane of Formula (1): R1aR2bSi(R3)4−(a+b)  Formula (1) [where R1 is an organic group of Formula (2): and is bonded to a silicon atom through a Si−C bond; R3 is an alkoxy group, an acyloxy group, or a halogen group; a is an integer of 1; b is an integer of 0 to 2; and a+b is an integer of 1 to 3], and a ratio of sulfur atoms to silicon atoms is 7% by mole or more in the whole of the silane. A resist underlayer film obtained by applying the resist underlayer film-forming composition onto a semiconductor substrate and baking it.