The formation of tetragonal BaTiO 3 from K 2 Ti 6 O 13 (K2T6) nanowires was examined under hydrothermal conditions at 100–240 1C. The morphology and the crystal structure of the BaTiO 3 particles that grew via a dissolution–precipitation mechanism were controlled by the temperature and the concentrations of the NaOH and the K2T6. The degree of tetragonality of the formed BaTiO 3 powders was quantitatively evaluated on the basis of a Rietveld crystal-structure refinement and compared with the results of Raman and DSC analyses. The powders consisted mainly of star-like BaTiO 3 particles that formed at 100 1C and contained cubic (22%) and tetragonal (78%) phases with a low c/a value of 1.0042. The BaTiO 3 particles changed their shape to dendritic and seaweed-like with an increase of temperature to 150 1C and 200–240 1C, respectively. According to the Rietveld analysis this increase of the temperature led to the formation of a tetragonal phase with a high c/a ratio (1.008–1.010), which dominated over the cubic and tetragonal phases with a low c/a (1.004–1.007). An increase in the K 2 Ti 6 O 13 and NaOH concentrations was found to decrease the tetragonality of the formed BaTiO 3 particles. The electron-diffraction patterns suggested a multidomain structure for the seaweed-like, mainly tetragonal, BaTiO 3 particles.