A flexible secondary battery includes an electrode assembly that includes a first electrode layer, a second electrode layer, and a separator that is disposed between the first electrode layer and the second electrode layer; a gasket that is flexible and surrounds an edge of the electrode assembly; a first sealing sheet that is attached to a first surface of the gasket; and a second sealing sheet that is attached to a second surface of the gasket opposite the first surface, wherein an uneven pattern is formed on a bendable area of the gasket.