La0.7La0.7Sr0.3Sr0.3MnO3−δMnO3−δ (LSM) magnetic properties are exploited through the application of a magnetic field, resulting in a significant decrease of the cathode polarization resistance, a crucial component of high temperature solid oxide fuel cells. The magnetic field is applied during the drying process after the deposition of LSM cathodes by screen-printing on a Gd0.1Gd0.1Ce0.9Ce0.9O1.95O1.95 (GDC) electrolyte. This specific process aims to decrease the cathode polarization resistance of solid oxide fuel cells. X-ray diffraction patterns show a structural modification triggered by the magnetic field. LSM cathode performance is investigated over a temperature range of 700–800 °C by impedance spectroscopy. The measured electrode area specific resistance (ASR) of a LSM/GDC/LSM symmetric half-cell without and with magnetic field was 0.30 ΩΩ cm2 and 0.20 ΩΩ cm2, respectively, at 800 °C. The ASR value was therefore decreased by 33% with the magnetic field effect. This behaviour may be attributed to LSM grain reorientation, microstructure change, and tortuosity modification of LSM cathodes.