Piezoelectric nanostructures have many important applications in nanodevices and micro-electro-mechanical systems. This work developed a topochemical method based on Molten-Salt Synthesis for synthesizing one-dimensional nanoscale single crystals of lead-free (K,Na)NbO3 (KNN) piezoelectric oxides. The synthesis process started from molten-salt reaction between Nb2O5 powders and KCl to produce high-aspect-ratio K2Nb8O21 bar-shaped particles which were transformed to Nb2O5 nanobars via ion-exchange and thermal decomposition steps, and finally, KNN nanobars were formed also by moltensalt reaction among Nb2O5 nanobars as templates, and K2CO3 and Na2CO3 in KCl salts. The as-synthesized KNN nanobars were proved to be single crystals by transmission electron microscopy. The piezoelectricity of an individual KNN nanobar was confirmed by scanning probe microscopy, as the effective piezoelectric coefficient d(33)* was measured to be 113 pm/V.