The transport properties of mixed conducting Sm0.5Sr0.5CoO3-delta (SSC) films featuring mean grain sizes from 44 nm to 4.42 mu m are studied with regard to grain-size effects. A remarkable enhancement in total conductivity of about one order is found in nano-scaled films than that of micro-crystalline films. In micro-crystalline films, a change in the transport mechanism as a function of temperature is observed, which is attributed to a transition from bulk controlled (at high temperatures) to grain-boundary controlled (at low temperatures) charge transportation. The films having nano-grains facilitates the charge transportation via parallel grain-boundaries and attribute to enhance the total conductivity through grain-boundaries. Alongside, the AC conductivity study showed that the charge carriers in nanoscaled films follow a long-range hopping path in the entire temperature region. Hence, the nano-scaled Sm0.5Sr0.5CoO3-delta cathodic films will give higher and steady state performance in solid oxide fuel cell (SOFC) in the low temperature region. (C) 2015 Elsevier B.V. All rights reserved.