A waterproof assembly for an electronic device includes a watertight door and a case. The watertight door includes a cover, a water absorbing ring, and a water blocking ring. The cover is provided for being disposed into an opening of the case. The water absorbing ring and the water blocking ring are disposed between an outer peripheral surface of the cover and an inner peripheral surface defining the opening. The water absorbing ring includes deformable material and water absorbent, such that the water absorbing ring expands by absorbing water and contacts the inner and outer peripheral surfaces. The water blocking ring is normally compressed and contacts the inner and outer peripheral surfaces. When water penetrating occurs, the water block ring blocks water preliminarily, and then the water absorbing ring block blocks fully water after completely expanding.