A refrigerator having a sub door which reduces energy loss and a method of manufacturing method the sub door. The refrigerator includes a main body provided with storage chambers formed therein, doors opening and closing the storage chambers, and provided with an opening, a sub door to open and close the opening, and a cooling unit provided on the rear surface of the sub door. When the sub door is opened, cool air of the cooling unit is transmitted to a stored article put on the rear surface of the sub door, and when the sub door is closed, relatively uniform temperature distribution in the storage chamber is achieved and thus storage performance of the refrigerator is improved.