A case for an electronic device includes a first housing, a second housing, a support and a sealing ring. The first housing has a first surface and a second surface that together form an accommodation portion. The second surface is connected to the first surface, and the second surface surrounds the first surface. The second housing is disposed in the accommodation portion. The second housing has a third surface and a fourth surface connected to each other. The third surface faces the first surface, and the fourth surface faces the second surface. The support is disposed between the first surface and the third surface for keeping a distance between the first surface and the third surface. The sealing ring is squeezed between the second surface and the fourth surface, and the sealing ring seals the accommodation portion.