A fuel cartridge for fuel cells is configured to include an inner bag made of a flexible material and filled with liquid fuel, a valve provided to the inner bag for discharging the fuel, and an outer case encasing the inner bag with the valve being exposed to the outside, the outer case being deformable by a hand and able to recover its initial shape by itself. The fuel cartridge allows the liquid fuel inside to be used almost completely irrespective of its attachment direction, and can be used in both applications where the cartridge is hand-pressed to discharge fuel and where fuel is pumped-out from the cartridge.