To provide a method of molding a nanocomposite resin capable of inexpensively forming a large quantity of an optical member excellent in optical characteristics using the nanocomposite resin containing inorganic particulates and a thermoplastic resin, and to provide a method of manufacturing a preform for the optical member comprising the nanocomposite resin.

The preform 1 includes the nanocomposite resin containing inorganic particulates and the thermoplastic resin and has protruded curved surfaces formed to the surface and back thereof. This preform 1 is formed through a process wherein a solution 2 containing the nanocomposite resin and at least one solvent which imparts flowability to the nanocomposite resin is arranged so as to impart an interface to a liquid phase 4 in which the nanocomposite resin is not dissolved and the gaseous phase superposed on the liquid phase 4, the first interface 2a of the solution 2 coming into contact with the liquid phase 4 and the second interface 2b of the solution 2 coming into contact with the gaseous phase are formed into protruded curved surfaces by interfacial tension and at least one solvent is removed from the solution 2 to gelatinize the solution 2.