The present invention provides an ink cartridge arranged on an ink jet printer, which comprises a housing having a wall and an opening; a cover for covering the opening of the housing; at least one ink chamber limited by the housing and the cover and provided with ink therein; an ink supply port formed on one wall of the housing opposite to the opening; and at least one recess formed on the outer surface of the cover and separated from the ink chamber. The recess forms a space when the ink cartridge is packed at a vacuum state. The pressure in the above space is lower than the atmospheric pressure.