A low refractive index film-forming composition and a low refractive index film are prepared with a method in which fluoroalkyl group-containing silicon alkoxide (B) is mixed with silicon alkoxide (A) to obtain a mixture; water (C), formic acid (D), and an organic solvent (E) are mixed with the mixture to produce a hydrolysate of the mixture; and silica sol (F) obtained by dispersing beaded colloidal silica particles in a liquid medium is mixed with the hydrolysate.