We present the results of ab initio hybrid density-functional calculations of the atomic and the electronic structures of LaMnO3 (LMO) and La1-xbSrxbMnO3 (001) surfaces. The total energies obtained from these calculations were used to analyze thermodynamic stability of the surfaces. We predict Sr and O vacancy segregation to the surface to occur with similar energies ( ˜0.5eV per defect). In pure LMO only MnO2 termination is thermodynamically favorable under typical operational conditions of a cathode in solid oxide fuel cells, whereas Sr doping makes La(Sr)O termination favorable. Finally, the role of Sr doping in cathode degradation is discussed.