There are a secondary battery having a pouch-type outer casing and a manufacturing method thereof. In one embodiment, a secondary battery includes an electrode assembly and an outer casing. The electrode assembly has positive and negative electrode plates, a separator interposed therebetween, and positive and negative electrode tabs having one ends respectively connected to the positive and negative electrode plates. The outer casing accommodates the electrode assembly so that the other ends of the positive and negative electrode tabs are extracted from a first side to the exterior thereof. The outer casing has a sealing portion sealed at least twice. The sealing portion is primarily sealed to be fractured under a predetermined internal pressure of the outer casing. After the aging of a battery, the sealing portion is fractured under the predetermined internal pressure, thereby exhausting internal gas. After the exhaustion of the internal gas, the sealing portion is secondarily sealed.