To efficiently manufacture a brookite type titanium oxide aqueous dispersion having a pH of about neutrality under mild conditions which is suitably used as a photocatalytic coating agent.

In making a raw material titanium compound into its peroxo compound and subjecting the obtained peroxotitanic acid solution to hydrothermal reaction, deionization treatment is performed before or after the peroxo step to adjust the ammonium ion concentration of the peroxotitanic acid solution to be supplied to the hydrothermal treatment step to ≤200 ppm, preferably ≤100 ppm and the pH to 6 or lower, preferably 3-5, and the hydrothermal treatment is performed at 85-150°C for 30 minutes to 10 hours to obtain the aqueous dispersion of titanium oxide containing a brookite type crystal. The photocatalytic coating agent is obtained by adding peroxotitanic acid to the obtained titanium oxide aqueous dispersion containing the brookite type crystal.