Provided is a composition formed by hydrolysis and condensation composition of the alkoxysilane, the composition comprising a reduced amount of metallic and halogen impurities and being applicable as electronic material. Also provided is an insulating film having low dielectric constant produced by applying the composition and sintering it. More specifically, a method for manufacturing a composition for forming a film, comprising a step of hydrolysis and condensation of alkoxysilane or a partial hydrolysis product of the alkoxysilane in an organic solvent in the presence of trialkylmethylammonium hydroxide as catalyst, wherein the alkoxysilane is selected from the groups consisting of compounds represented by formulae (1) to (4) below, and the trialkylmethylammonium hydroxide is represented by formula (5) below. Provided are a composition for forming a film obtained by the method, and a low dielectric constant film having low metallic and halogen impurities, the film produced by applying the composition for forming a film on a substrate and sintering it. ##STR00001##