A key structure includes a keycap, a scissors-type connecting element, a first knocking part, a resilience element and a second knocking part. The scissors-type connecting element is coupled to a bottom surface of the keycap. The scissors-type connecting element includes an inner frame and an outer frame. The first knocking part is disposed within a space surrounded by the inner frame. The resilience element is located under the first knocking part. The second knocking part is coupled to the bottom surface of the keycap and faces the first knocking part. While the keycap is pressed down, the second knocking part knocks on the first knocking part, and the first knocking part is moved downwardly. When the keycap is not pressed down, the first knocking part is moved upwardly and returned to an original position in response to an elastic force of the resilience element.