Provided is a film having a low
refractive index, which can be formed under normal
temperature and pressure while obtaining a lower
refractive index, has excellent adhesion with a
solid substrate, and does not lose geometric optical properties, such as the diffusibility or light-harvesting capability attributed to the
microstructure. Also disclosed is a method for producing the same. The film having a low
refractive index is obtained by causing an
electrolyte polymer and microparticles to be alternately adsorbed on the surface of a
solid substrate and bringing the resulting
microparticle-laminated film into contact with a
silicon compound solution in order to bond the
solid substrate with microparticles and microparticles with microparticles. The
silicon compound solution is selected from (1) the
hydrolysis product of alkoxysilane (I) wherein the functional groups are formed from hydrolyzable groups and non-hydrolyzable organic groups, and the
condensation reaction product thereof, (2) the
hydrolysis product of a mixture of alkoxysilane (I) and alkoxysilane (II) wherein the functional groups are formed from hydrolyzable groups alone, and the
condensation reaction product thereof; and (3) a mixture of
hydrolysis product and condensation product thereof according to (1) and alkoxysilane (II).