Abstract Sodium potassium tungsten bronzes, NaxKyWO3, having various values of x and y were prepared by electrolytically treating a fused mixture of carbonates of the two alkali metals and tungsten-(VI) oxide. Lattice constants, a and c, of the tetragonal crystals were estimated by the X-ray powder method. Similarity of the crystal lattice of these bronzes to that of potassium tungsten bronzes, instead of to that of sodium tungsten bronzes, suggests that the lattice constants of the sodium potassium bronzes are by far more influenced by the potassium content than by the sodium content.