Provided are a method for easily and quickly producing a patterned thin film having a high refractive index and a high transparency, and a highly refractive thin film produced by the method. The method comprises a first step: a step of forming, on a substrate, a coating using a sol containing a metal oxide modified with a phosphorus compound represented by the following formula (1): (wherein R1 is a hydrogen atom, an alkyl group, an alkynyl group, an alkenyl group, an aryl group, an aliphatic heterocyclic group, or an aromatic heterocyclic group; R2 is a divalent organic residue; and n is 1 or 2); a second step: a step of curing the coating on the substrate obtained in the first step by light irradiation; and a third step: a step of further adding energy to the cured film obtained in the second step by heating and/or light irradiation.