A key structure includes a base plate, a key cap, a scissor, a spring, a positioning base, a first cover and a second cover. The key cap is disposed above the base plate. The scissor, the spring, the positioning base, the first cover and the second cover are located between the base plate and the key cap. The scissor abuts against the base plate and the key cap. The spring abuts against the key cap. The positioning base is connected to the key cap, wherein the positioning base has a positioning groove and a part of the spring is located in the positioning groove. The first cover is connected to the positioning base, wherein the first cover has a through hole overlapped with the positioning groove, and the spring penetrates the through hole. The second cover is slidably connected to the first cover. The second cover penetrates the through hole and abuts against the base plate, and another part of the spring abuts against the second cover and is covered by the second cover.