Abstract: An external keyboard of an electronic device having a capacitive touch screen and a connector socket is provided. The external keyboard includes a keyboard body and a plurality of physical buttons. The keyboard body is for being disposed on the capacitive touch screen and includes a connector connected to the connector socket. Each physical button has a trigger portion, and a top surface and a bottom surface opposite to each other, and the trigger portion is disposed between the top surface and the bottom surface. The physical buttons are disposed in the keyboard body at intervals. When a distance between the trigger portion and the capacitive touch screen is less than a trigger interval, capacitance of a region of the capacitive touch screen corresponding to the trigger portion is changed by the trigger portion to generate a touch signal. Furthermore, a sheath of an electronic device is also provided.