The present invention relates to a cap assembly and a battery including the same. More particularly, the present invention relates to a cap assembly for a cylindrical secondary battery, in which the support unit of a current interrupt device (CID) is seated in the inclined portion or the terraced portion of a gasket and thus the battery is dually sealed, thereby preventing the leakage of an electrolyte, and a cylindrical secondary battery including the cylindrical secondary battery. The cap assembly of the present invention is dually sealed for the leakage of an electrolyte. Accordingly, there is an advantage in that the safety of the battery can be greatly improved because the electrolyte is rarely leaked although the battery is shocked because of dropping.