Novel polycrystalline Ni0.5Zn0.5Sm0.025HoxFe1.975-xO4 (x = 0-0.06) ferrites were fabricated by a traditional solid-state reaction sintering method. The codoping effects of Sm and Ho on the microstructure, magnetism, and high-frequency performance of Ni-Zn ferrites were investigated. The substitution of Sm3+ and Ho3+ ions led to an apparent increase in the lattice constants. However, further increasing the addition of both dopants introduced SmFeO3 or HoFeO3 foreign phases at the boundaries of the polycrystalline grains. As the content of Ho3+ ions increased, the relative density and average grain size of the specimens decreased accordingly. Moreover, the substitution of Sm3+ clearly decreased the saturation magnetization and complex permeability, which further decreased with the doping of Ho3+. The evolution of the Curie temperature showed an opposite trend, reaching the highest temperature of 278 degrees C when x = 0.03. Similarly, the coercivity and resonance frequencies also displayed opposite trends compared to those of the saturation magnetization and complex permeability. The codoping of Sm3+ and Ho3+ more effectively lowered the magnetic and dielectric loss tangent of the specimens compared with the undoped or single dopant modified ferrites.