A needle-like NaNbO3 polycrystal was synthesized successfully from Na3NbO4 at low temperatures by the dissolution-precipitation method. The Na3NbO4 precursor could be dissolved in an aqueous solution, and the Nb6O198- cluster was formed. When the pH of the solution was above 13, needle-like Na-7(H3O)Nb6O19 center dot 14H(2)O crystals were precipitated, which were 0.25-0.55 mu m in width and more than 2 mu m in length. When heated at a low temperature of 500 degrees C, the needle-like Na-7(H3O)Nb6O19 center dot 14H(2)O crystals transformed to the needle-like NaNbO3 polycrystal. The excess Na could be washed out with water.