Mn oxide supported on two different groups of titania, hydrous or crystalline titanium oxide, were investigated for the selective catalytic reduction of NOx with NH3 (NH3 SCR). Hydrous titania was prepared by hydrolysis of titanium tetraisopropoxide followed by drying, and crystalline titanium oxide was prepared with further calcination of the hydrous titania. Mn supported on hydrous TiO2 catalyst exhibited higher NOx conversion over wide temperature range (150–400 °C) as well as the suppressed formation of nitrous oxide compared to Mn supported on crystalline TiO2. Also, Mn/hydrous TiO2 showed relatively lower performance in ammonia oxidation than Mn/crystalline TiO2 which is regarded as the side reaction. Several combined characterization results indicate that manganese species more strongly interact with hydrous TiO2 than crystalline TiO2, resulting in different redox behavior and oxidation state of Mn oxides. It can be concluded that the activity and selectivity of Mn/TiO2 catalysts in NH3 SCR reaction were affected by initial state of titania support.