High-frequency soft magnetic ferrite ceramics are desired in miniaturized and efficient power electronics but remain extremely challenging to deploy on account of the power loss (P_cv) at megahertz frequencies. Here, we prepared NiCuZn ferrite with superior high-frequency properties by V₂O₅ and Bi₂O₃ synergistic doping, which proves to be a potent pathway to reduce P_cv of the ferrite at megahertz frequencies. The sample doped with 800 ppm V₂O₅ and 800 ppm Bi₂O₃ yielded the most optimized magnetic properties with a P_cv of 113 kW/m³ (10 MHz, 5 mT, 25 ℃), an initial permeability (μ_i) of 89, and a saturation induction (B_s) of 340 mT, which is at the forefront of the reported results. These outstanding properties are closely related to the notable grain boundary structure, which features a new type of nano-Bi₂Fe₄O₉ phase around ferrite grains and a Ca/Si/V/O amorphous layer. Our results indicate great strides in correlating the grain boundary structure with multiple-ion doping and set the scene for the developing high-frequency soft magnet ferrites.