|Cation segregation in the perovskite oxide surfaces has been commonly observed in a range of applications including solid oxide fuel cells, batteries, oxygen permeation membranes, magnetic and ferroelectric materials. In particular, the precise control of surface composition and structure is crucial to tailor the catalytic activity of transition-metal oxides, and hence to improve the reactivity and stability of the solid oxide fuel cell cathodes. However, while significant efforts have been directed to understanding this phenomenon, the mechanism that explains the physical origin of the cation rearrangements remains unclear. A unified theory for the cation segregation is therefore needed for designing optimal materials with enhanced cathode performance. This talk presents 1) the systematic assessment of the driving forces for cation rearrangements in manganite-based perovskite oxides, and 2) the enhanced cathode stability with a control of segregation on the surfaces.