Complete liquidus and solidus equilibria have been established by DTA and quench techniques in the system NaNbO3BaNb2O6, which contains the pseudo-tetragonal bronze NaBa2Nb5O15. While little solid solution occurs in the end member compounds, the tungsten bronze phase shows extensive solid solubility from 62 to 83 mole % BaNb2O6. These results and subsolidus DTA and dielectric measurements are discussed in relation to the crystal chemistry of the bronze structure. The essential features of the phase diagram have been confirmed by Czochralski crystal growth experiments at selected melt compositions in the bronze(ss) field. © 1969.