Systematic microstructural analyses have been carried out on a series of technological SOFCs that went through long-term cell tests with various operating parameters including temperature, current load and time length under current. For the LSM-YSZ cathode, a number of microstructure degradation mechanisms have been identified. And it has been observed that different mechanisms dominate the degradation process under different test conditions. The severe cathode degradation at 750 degrees C operation with high current density is attributed to a loss of the cathode/electrolyte interface stability. For the cells tested at 850 degrees C, the interface stability is maintained due to further sintering during cell operation. A cell test lasting for 2 years (17500 h) at 850 degrees C with a moderate current density (not greater than 1 A/cm(2)) has shown that the cathode microstructure is fairly robust to the degradation processes at this temperature, such as grain coarsening and element diffusion. The cell degrades mildly with a cell voltage degradation rate of 7 mV/1000 h. (C) 2011 Elsevier B.V. All rights reserved.