NaNbO3 with a cubic phase was synthesized under extremely mild conditions. Sodium niobates represented by Na7(H3O)Nb6O19·14H2O and Na2Nb2O6·H2O were formed as precursors by alkaline treatment of amorphous Nb2O5 under ambient conditions, which were converted to crystalline NaNbO3 by simple calcination at 500 °C. In addition, the morphology of the obtained NaNbO3 was affected by alkaline treatment time.