Innovative concepts for novel electrode structures have been actively pursued over recent years to achieve both superior electrochemical performance as well as long-term stability for the development of solid oxide cells (SOCs) with efficient energy conversion. In this study, towards understanding the role of surfaces and interfaces on electrochemical performance and long-term stability of nanostructured La0.6Sr0.4CoO3−δ (LSC) thin film electrodes, a systematic investigation of the effect of deposition temperature and long-term annealing was conducted. The surface conditions of the LSC thin films, in terms of the proportion of surface-bound Sr and valence state of Co, are highly influenced by the deposition temperature; however, prolonged annealing at 700 °C in air of LSC thin films deposited at various temperatures essentially transforms their surfaces to a final state having similar chemical environment and crystalline properties. On the other hand, Sr diffusion across the LSC/GDC interfaces is promoted at higher deposition temperatures and is further accelerated with prolonged heating at 700 °C. Significant improvement in the electrochemical performance for symmetrical cells using LSC thin films is attributed to two main factors: enhancement of the surface exchange property as mediated by a distinctive nanostructure that allows the retention of a high porosity, and better stability of the electrode–electrolyte interfaces owing to the suppressed cation diffusion. This work paves the way to obtaining highly active and durable electrodes through tuning surfaces and interfaces and provides guidance for designing novel electrode materials with excellent performance for SOC applications.