A stack for a mixed oxidant fuel cell and a mixed oxidant fuel cell system including the stack. The stack includes at least one membrane-electrode assembly that includes a polymer electrolyte membrane, an anode and a cathode disposed on opposite sides of the polymer electrolyte membrane, and an electrode substrate disposed on at least one of the anode or the cathode; and an oxidant supply path and a fuel supply path that penetrate the membrane-electrode assembly. The oxidant supply path has both ends open, and the fuel supply path has one end open and the other end closed. The stack of the present invention can improve fuel cell efficiency by smoothly supplying a fuel and an oxidant. Particularly, since the stack is configured to supply the fuel and the oxidant without using a pump, it can make a fuel cell small and light.