Mechanical connections between a fixing member, a bare secondary battery cell and a protection circuit module by pressurizing a bare cell by a fastening member are disclosed. The secondary battery is capable of stably fixing an upper case and the bare cell. The secondary battery may include a bare cell including an electrode assembly in the inside thereof and formed with a fixing groove in both sides of a top surface; a protection circuit module electrically connected to the bare cell; and an upper case surrounding the protection circuit module and formed with the fastening hole in the position corresponding to the fixing groove. A bottom surface of the upper case not formed with the fastening hole may be formed with an adhering portion contacting the top surface of the bare cell and a space portion not contacting the top surface of the bare cell.