The activation behavior of a LSM based-cathode in the SOFC is characterized by a rapid reduction in the electrode polarization resistance after cathodic current passage treatment. This activation behavior has been attributed to mechanisms that either enhance the kinetics of oxygen reduction or remove impediments from the oxygen reduction mechanism. Due to the sensitivity of the activation process to the operation history, a comprehensive study was carried out to reveal the relationship between the activation conditions, the steady state cathode performance and the long term stability. This work demonstrates the application of a two electrode configuration half-cell operated for the impedance analysis of LSM-based electrodes. The effects of current density and overpotentials on the activation behavior of LSM based electrode were investigated. The impacts of temperature and oxygen partial pressure to the activation process and final performance are also discussed. Long term degradation test of LSM electrodes were carried out on both half-cells and full cells with various activation processes. Numerical simulation of the LSM-based cathode was conducted with a multi-step oxygen reduction reaction (ORR) mechanism for a better understanding of the nature of the activation process. The results are of great relevance as the electrode performance depends on not only the fabrication but also on the initial break-in procedure.