In this study, pellet samples of Na_1-xK_xNbO₃ (NKN) (0.160 ≤ x ≤ 0.200) were prepared using the solid-state reaction method with double sintering. For the prepared compositions, the dielectric measurements were carried out from room temperature to 480 °C, at 10, 100, and 1000 kHz. Dielectric measurements of the prepared samples indicated anomalies around 210, 380, and 450 °C. High temperature X-ray diffraction (HT-XRD) measurements were carried out to analyze the structural properties of the samples, with x = 0.175. Consistent with the dielectric behavior, HT-XRD measurements of the prepared samples, with x = 0.175, indicated monoclinic phase, between room temperature and 210 °C; tetragonal phase, between 210 and 380 °C; tetragonal phase with a change in the lattice, between 380 and 460 °C; and cubic phase above 460 °C, in the measured temperature range.