Anatase nano titanium oxide was synthesized with Ti(SO4)2 as titanium source and stronger ammonia water as precipitant using the hydrothermal method. The samples were characterized by XRD, SEM, TEM and UV-VIS. The results showed that the influence of the increase of the reaction time on as-prepared anatase nano titanium oxide was not obvious when stronger ammonia water was not added to Ti(SO4)2 solution. Anatase nano titanium oxide became small markedly under the same conditions when stronger ammonia water was added to Ti(SO4)2 solution. Anatase nano titanium oxide of about 20 nm in the diameter was obtained for 48 h with pH=9 at 240 °C by the hydrothermal method. That the size of Anatase nano titanium oxide particles became small was propitious to the blue shift of their absorption peak.