A keyboard device includes plural key structures. Each key structure includes a supporting plate, a keycap, a connecting member and a hook element. The keycap is located over the supporting plate, and movable upwardly or downwardly relative to the supporting plate. The connecting member is connected between the supporting plate and the keycap. The hook element is installed on the supporting plate. The connecting member is connected with the supporting plate through the hook element. The supporting plate is made of a first material with a first specific gravity. The hook element is made of a second material with a second specific gravity. The second specific gravity is higher than the first specific gravity.