The invention discloses an electronic device and a casing thereof. The casing of the electronic device comprises: a casing and a button; at least one mounting hole is formed on the side wall of the casing; the button comprises: a button body and at least one convex A column, the convex column is arranged on one side of the button body, the convex column includes: a first shaft segment and a second shaft segment, the first shaft segment is connected with the button body, the second The shaft segment is connected to the side of the first shaft segment away from the key body, a first stepped surface is formed between the first shaft segment and the second shaft segment, and the first shaft segment is connected to the The installation holes are in interference fit, the second shaft segment protrudes into the casing through the installation holes, and the first step surface and the inner end face of the casing are arranged in abutment. Therefore, the electronic device has good sealing performance, and requires fewer parts during manufacture of the casing, the overall assembly is simple, and the manufacturing cost is low.