Abstract: With nitrates and ethylene diamine tetra acetic acid (EDTA) as precursors, La₂Ni_1-xFe_xO_4+δ powder was prepared by sol-gel method.XRD results indicate that the complex oxides have K₂NiF₄ structure.The iodometric titration was used to determine both the oxidation state of Ni/Fe ions and the oxygen nonstoichiometry in La₂Ni_1-xFe_xO_4+δ.It has been found that the both mentioned above will increase with the increase of coefficient x.The oxygen nonstoichiometry reached at 0.2462 when x=0.2.FT-IR spectrums revealed that the induced Fe may strengthen the Ni-O bond asymmetric vibration, which facilitates the mobility of non-stoichiometric interstitial oxygen ion in the lattice.AC impedance spectroscopy measurements were used to study the ionic conductivity.The ionic conductivity increases with the increase of coefficient x.The changes of conductivity with temperature below 650℃ are in accordance with the conduction mechanism of small polarons.