Abstract: NiFe2O4 spinel samples with different mass fractions of MnO2 were synthesized by two-step solid phase sintering process. The morphology and phase transformation were examined by scanning electron microscopy, X-ray diffraction and DTA analysis, respectively. The sintering behavior and magnetic property were investigated by thermal expansion instrument and vibrating sample magnetometer, respectively. The results showed that MnO2 decomposes into MnO and Mn2O3, the crystalline structure of the ceramic matrix is still of NiFe2O4 spinel and no other new phases appear. MnO2 addition can promote sintering obviously, the temperature where maximum shrinkage rate is attained for 1% MnO2-doped samples is 59°C, lower than that for un-doped samples. The saturation magnetization and coercivity are 15.673 emu/g and 48.316 Oe, respectively for 1% MnO2-doped samples.