Disclosed are a secondary battery and a method of manufacturing the same. The method of manufacturing a secondary battery includes preparing a pouch case comprising a first case and a second case, seating an electrode assembly into the first case, covering the first case comprising a receiving part with the second case, and sealing a side portion of the first case and a side portion of the second case using a jig. The jig includes a first jig compressing the first case and a second jig compressing the second case. A first compressed width of the first case compressed by the first jig is less than a second compressed width of the second case compressed by the second jig.