An ink cartridge is disclosed and includes a hollow ink tank body, a cover member connected to the body, a pressure regulator mounted on the bottom of the body, a tank disposed under the body and connected to the bottom thereof, and a hollow tube. The body is defined with a cavity therein and an outlet port formed on a bottom thereof. The cover member has a filling inlet and an air vent formed thereon. The tank corresponds to and communicates with the pressure regulator, and further has a venthole and a porous member disposed therein. The hollow tube communicates with the air vent of the cover member and the venthole of the tank. Therefore, the atmospheric air passes into the body via the hollow tube and the tank.