Provided is a locking device for an internal battery pack cover of a mobile phone, which is mounted on a lower case frame of a main body of the mobile phone, and which includes a locking member formed on the lower case frame; and a locking module coupled to the cover and rotating around a hinge axis with a sliding movement of a button unit to be mounted within or released from the lock member, thereby causing the cover to be coupled to or detached from the main body.