The DC-bias superposition characteristics of NiCuZn ferrite with different amount of Bi2O3 have been investigated. The microstructure depends much on the amount of Bi2O3. The DC-bias-superposition characteristics have great relationship with the microstructure. The permeability of materials composed of tiny grains decreases more slowly with the increase of DC-bias superposition due to the absence of the domain walls in the grain. The nonmagnetic phase in the grain boundary can reduce the actual DC-bias superposition in the grains when the sample was subject to DC-bias superposition. In short, a microstructure with relatively small average grain size and thick nonmagnetic phase in the grain boundary, which is favorable for obtaining better DC-bias superposition characteristics.