The relationship between magnetic domain structures and magnetic properties of Nd-doped Sm(Fe, Cu, Zr, Co) 7.5 was investigated. In the preparation process, slow cooling between sintering and solution treatment was employed to promote homogenization of microstructures. The developed magnet achieved a maximum energy product, [ BH ] m , of 33.8 MGOe and coercivity, ${H} _{\mathrm {cb}}$ , of 11.2 kOe at 25 °C, respectively. Moreover, ${B}$ – ${H}$ line at 150 °C was linear, which means that irreversible demagnetization does not occur even at 150 °C. Temperature coefficients of remanent magnetic flux density, ${B} _{r}$ , and intrinsic coercivity, ${H} _{\mathrm {cj}}$ , were 0.035%/K and 0.24%/K, respectively, as usual the conventional Sm–Co magnet. Magnetic domain structures were observed with a Kerr effect microscope with a magnetic field applied from 0 to −20 kOe, and then reverse magnetic domains were generated evenly from grain boundaries. Microstructures referred to as “cell structures” were observed with a scanning transmission electron microscope. Fe and Cu were separated to 2–17 and 1–5 phases, respectively. Moreover, without producing impurity phases, Nd showed the same composition behavior with Sm in a cell structure.