Provided is a coating liquid for forming a porous film having desirably controlled thickness and having excellent dielectric and mechanical properties, using the conventional semiconductor process. Specifically, provided is a composition for forming a porous film comprising a condensation product and an organic solvent wherein the condensation product is obtained by hydrolysis and condensation, at presence of a basic catalyst, ofone or more silane compounds represented by formula (1): R.sup.1.sub.kSi(OR.sup.2).sub.4-k,and one or more crosslinking agents represented by formula (2): {X.sub.j(Y).sub.3-jSi-(L).sub.m-}.sub.nMZ.sub.4-n.Moreover, a method for manufacturing a porous film comprising steps of applying said composition so as to form a film, drying the film and heating the dried film so as to hardent the film, and others are provided.