A key structure includes a keycap, a membrane circuit board, and a rubber dome between the keycap and the membrane circuit board. The rubber dome includes a ring-shaped structure, a lower foundation structure, a contacting post, a first inclined wall and a second inclined wall. The ring-shaped structure includes a first top surface. The first top surface is upwardly pushed against the keycap. The lower foundation structure includes a first bottom surface. The first bottom surface is pushed downwardly pushed against the membrane circuit board. The contacting post is connected with the ring-shaped structure. The first inclined wall is connected with the ring-shaped structure and the lower foundation structure. The second inclined wall is connected with the ring-shaped structure and the contacting post. There is a first included angle θ1 between the second inclined wall and the first bottom surface. Preferably, 30°≤θ1≤85°.