An attachable assembly for smart phone that has at least one contact site disposed thereon is disclosed. The attachable assembly comprises a mount unit and an extension device. The mount unit is fixed at one edge of the smart phone, and has at least one locking slot disposed thereon; the extension device electrically contacts the contact site and has at least one locking member selectively engaged to the locking slot. Wherein, the extension device has a rotative axis so that the extension device is rotated and fitted with the mount unit.