A separator for a battery includes a first separating layer for preventing a short circuit between a positive electrode and a negative electrode and a second separating layer having higher electrolyte retaining power than the first separating layer. The second separating layer is attached on the first separating layer. The second separating layer is made of polyethylene terephtalate, and the first separating layer is selected from the group consisting of nylon and polypropylene. Preferably, the first separating layer is attached on the second separating layer through a thermal fusing process.