We synthesized La0.75Sr0.25FeO3 (LSF) using Glycine Nitrate Process (GNP) method. After that in order to create additional oxygen vacancies, A-site deficiency was introduced intentionally into the mixed conducting perovskite ABO3-type oxide. So, we synthesized and investigated (La0.75Sr0.25)1-xFeO3-δ perovskite oxides having different stoichiomety (x=0, 0.02, 0.04, 0.06, 0.08). The micro structure, electrical conductivity and electrocatalytic activity of the electrodes were evaluated by X-ray diffraction (XRD) analysis, 4-probe DC-conductivity measurement technique and AC impedance spectroscopy, respectively. From the analysis of SEM images and XRD patterns, we realized that the synthesized powder has uniform size distribution and high degree of crystallinity. Both the electric conductivity and the electrocatalytic activity is strongly influenced by the amount of A-site deficiency in LSF, and those properties had highest value at the stoichiometry x=0.02. The electric conductivity and the electrocatalytic activity of the synthesized materials were discussed in terms of the microstructural change caused by the variation of oxygen vacancy.