(57) The present invention provides: a coating composition for forming a titanium oxide film, comprising (A) a titanium-containing aqueous liquid obtained by mixing at least one titanium compound selected from the group consisting of hydrolyzable titanium compounds, low condensates of hydrolyzable titanium compounds, titanium hydroxide and low condensates of titanium hydroxide with aqueous hydrogen peroxide, and (B) at least one halide selected from the group consisting of titanium halides, titanium halide salts, zirconium halides, zirconium halide salts, silicon halides and silicon halide salts;
a process for forming a titanium oxide film, comprising applying the coating composition to a metal substrate and drying the resulting coat; and
an undercoating material for metal substrates and a post-treating agent for phosphate undercoats on metal substrates, the material and agent being the above coating composition.