The structure and temperature stability of high-temperature permanent magnets Sm(Co0.796−xFe0.177CuxZr0.027)6.63 (x = 0.117 and 0.130) were studied using x-ray diffraction analysis, thermomagnetic analysis, and scanning and transmission electron microscopy. The magnets have a nanocrystalline cellular structure composed of the R2:17 cell phase, 1:5 boundary phase (27–28% by volume), and Z-phase platelets. The 1:5 phase is formed in the course of isothermal annealing at 850°C and exists in the entire temperature range from 850°C to 400°C. The Curie temperature of the R2:17 and 1:5 phases is approximately 815°C and 580°C, respectively. The magnets have the following hysteresis properties at room temperature: Br = 890–920 mT, JHc = 2.4–2.6 MA/m, BHc = 629–676 kA/m, and (BH)m = 143–159 kJ/m3. In the temperature range of 20–500°C, the temperature coefficients of Br and JHc of the magnets (x = 0.117 and 0.130) do not exceed |− 0.070| and |− 0.172|%/°C, respectively. © 2018, The Minerals, Metals & Materials Society.