A key structure, including a keycap, a scissor component, an elastomer, an optical switch, a shading portion, and a circuit board, is provided. The scissor component is formed of a first and a second supporter. The circuit board has two first and two second limiting units. The keycap has two third and two fourth limiting units. The first supporter is rotatably or slidably connected to the first and the third limiting units. The second supporter is rotatably or slidably connected to the second and the fourth limiting units. The keycap is disposed on the circuit board through the scissor component. The elastomer is interposed between the circuit board and the keycap. The optical switch includes an emitter and a receiver. The shading portion is disposed on the first or the second supporter to block a light signal transmitted between the emitter and the receiver.