A composition for a resist underlayer film is provided. The composition has excellent storage stability and can form a resist underlayer film which has excellent adhesion to a resist film, can improve reproducibility of a resist pattern and is resistant to an alkaline liquid used in development and to oxygen ashing during the removal of a resist. The composition comprises a hydrolyzate and/or a condensate of a silane compound of the following formula (A), R1bR2cSi(OR3)4-a  (A) wherein R1 is a monovalent organic group having at least one unsaturated bond, R2 individually represents a hydrogen atom, a halogen atom or a monovalent organic group, R3 individually represents a monovalent organic group, R1 is a group other than OR3, a is an integer of 1 to 3, b is an integer of 1 to 3, and c is an integer of 0 to 2, provided that a=b+c.