Disclosed herein is a secondary battery comprising electrode leads mounted in a sealed fashion in a battery case while the electrode leads partially protrude from the battery case and resin films disposed between the battery case and the electrode leads wherein the electrode leads are provided at predetermined areas of the surfaces thereof, to which the resin films are applied, with irregular parts, by which the adhesive strength between the electrode leads and the resin films is increased. The adhesive strength between the electrode leads and the resin films is large, and the movement path of moisture or electrolyte, through which the moisture contained in the air or the electrolyte contained in the secondary battery may move, is extended. Consequently, the present invention has the effect of minimizing the reduction in service life of the secondary battery due to introduction of the moisture into the secondary battery and leakage of the electrolyte from the secondary battery. The secondary battery is very useful as a unit cell for medium- or large-sized battery systems, such as hybrid electric vehicles.