To provide a method of producing a porous film having a high film strength and a low refractive index while maintaining porosity, and an anti-reflection film having a low refractive index.

The method of producing a porous film composed mainly of silica includes: a process to apply and dry on a substrate a sol reactive liquid containing organic matter, silica precursor materials, alcohol, catalyst made of acid or base, and water; a process to calcine the substrate, remove the organic matter and form a silica porous film on the substrate; and a process to perform UV ozone treatment to the silica porous film. The anti-reflection film is provided having a porous film obtained by the production method.