An optional element having a cured coating film on optical base material wherein the cured coating film is prepared with a coating composition comprising an organosilicon compound and modified stannic oxide-zirconium oxide composite colloidal particles which are obtained by partially or fully coating the surface of stannic oxide-zirconium oxide composite colloidal particles with tungstic oxide-stannic oxide composite colloidal particles. The formed cured coating film is excellent in hot water resistance, and light-resistance and weathering resistance are not impaired even when the antireflection film made by vepor deposition of inorganic oxides is applied on the cured coating film.