$La_{0.5}Sr_{0.5}MnO_{3-delta}$ as air electrode for soild oxide fuel cell was synthesized by a citrate process and its cathodic polarization was determinated by the current interruption method on the Gd-doped ceria as electrolyte. The addition of citric acid increased the exothermic heat for the formation of $La_{0.5}Sr_{0.5}MnO_{3-delta}$ perovskite oxide. The degree of the initial particle agglomeration was affected by the exothermic heat. Also the increase of cal-cination temperature enlarged the particle size and the higher sintering temperature accelerated the den-sification of $La_{0.5}Sr_{0.5}MnO_{3-delta}$ layer after its being painted on $Ce_{0.8}Gd_{0.2}O_{1.9}$ electrolyte. In this study $La_{0.5}Sr_{0.5}MnO_{3-delta}$ synthesized by citrate process of which the molar ratio of citric acid to metal nitrate was 2 calcined at $650^{circ}C$ for 2hr and sintered at 1100 at $1200^{circ}C$ for 4 hrs after slurry coating on Ce0.8Gd0.2O1.9 electrlyte showed the lowest cathodic polarization.