Process for formation of tin oxide film

A process for formation of a tin oxide film, wherein a glass substrate is heated to a high temperature of from 450.degree. C. to 600.degree. C. and then a tin oxide film is formed on the surface of said substrate by a thermal decomposition oxidation reaction caused by bringing a tin compound or a mixture of a tin compound and a fluorine-containing compound into contact with the surface of said glass substrate, and wherein prior to the formation of said tin oxide film, said glass substrate is preliminarily brought into contact with a solution of chloride of a metal belonging to Group IVB of the Periodic Table so that a layer of a composition containing the chloride of the Group IVB metal as the primary component is formed on the surface of said substrate wherein the chloride of the group IVB is contained in said solution in an amount of from 0.1 to 10.0 wt. %.