The secondary battery includes an electrode assembly including a first electrode plate and a second electrode plate whereon first and second electrode active materials, and first and second electrode tabs are formed, respectively, and including a separator disposed between the first and second electrode plates while overlapping with the first and second electrode plates; and a planarizing member disposed on at least one of first and second ends that are opposite to each other in a longitudinal direction of the electrode assembly, wherein the planarizing member covers a stepped surface exposed on the at least one of the first and second ends so as to planarize the stepped surface. In the secondary battery, the stepped surface of an end of the electrode assembly is planarized.