Well-developed cubic crystals of NaTaO₃ and NaTaO₃ : La were successfully grown by cooling an NaCl flux at 650–1000 °C. Colourless and transparent NaTaO₃ and NaTaO₃ : La crystals were obtained from relatively low-temperature solutions containing 20 mol% solute, with a smallest average size of 0.18 μm. The crystal sizes and forms were highly dependent on the holding temperature, cooling rate, and starting composition. In particular, when La₂O₃ powders were added to the starting compositions, NaTaO₃ : La crystals with a very unique surface morphology were grown from the NaCl flux. Additionally, the average size of the NaTaO₃ : La crystals decreased dramatically when compared with that of the NaTaO₃ crystals prepared under the same conditions. Furthermore, the NaTaO₃ and NaTaO₃ : La crystals exhibited high dye photodegradation activity. These results demonstrate that NaCl is adequate for synthesizing high quality and well-developed tantalate crystals.