In synthetic TiO2, anatase to rutile transformation usually occurs at a temperature over 550 degrees C. Here, we report a silica-protection method that can extend the phase transformation temperature to 800 degrees C. This approach involves the deposition of silica shells on TiO2 microspheres and subsequent calcination in either air or ammonia, yielding core-shell microspheres. Nitridation of the silica-coated TiO2 using ammonia gas transformed the amorphous TiO2 core into crystalline N-doped TiO2 (TiO2-xNx), while rendering the silica shell mesoporous. The anatase TiO2-xNx phase could be retained at 800 degrees C due to the silica shell. The nitrided microspheres with anatase phase exhibited excellent photocatalytic activities for the degradation of organic pollutants and high photo-electrochemical performance in producing photocurrents under visible-light irradiation. Moreover, the nitrided anatase TiO2-xNx retained its high photocatalytic activities even after one and half years of exposure to air. Thus, the silica-protection method is a simple and effective strategy for the synthesis of high-temperature stable N doped anatase TiO2 photocatalysts with sustainable photocatalytic activities.