A secondary battery includes an electrode assembly in which a cathode plate and an anode plate are arranged with a separator being interposed therebetween, a case in which the electrode assembly is received, a cap assembly capable of sealing an open end of the case, a gasket interposed between the case and the cap assembly, and a leakage prevention portion formed at one surface of the gasket and/or one surface of the cap assembly, which is oriented toward the electrode assembly and contacted with the gasket.