A door assembly disposed at an opening of a casing of an electronic device is provided. An insertion hole provided at a side of the casing close to the opening for an pin to be inserted into the casing through the insertion hole. The door assembly includes a door cap and a rejecting module. The door cap is at least partially connected to the casing and corresponding to the opening. The rejecting module is disposed in the casing and corresponding to the door cap. The rejecting module is configured to push the door cap to expose the opening when the pin is inserted into the casing through the insertion hole. An electronic device is also provided, which includes a casing and the door assembly.