The solid state interdiffusion between NiFe2O4 and NiO in nitrogen atmosphere was studied by means of diffusion couple technique.NiFe2O4/NiO diffusion couple with plane interfaces was made by clamping method and sintering at 1 300 ℃ for 10 h.Scanning electronic microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS) were used to analyze the microstnlcture and phase composition of the diffusion couples.The results indicate that a porous layer of uniform thickness forms along the NiFe2O4/NiO bonding interface and exhibits a deep penetration in the NiFe2O4 due to the Kirkendall effect.Furthermore,SEM observations reveal that the needle-like nickel ferrite precipitates form in NiO near the interface and the formation mechanism of them are inferred to be diffusion type solid-state phase changes.