Giant magnetic liposomes (diameter up to 40 mu m) have been synthesized. They are constituted by an aqueous magnetic fluid at pH 7 encapsulated in phospholipids vesicles. When they are submitted to a magnetic field, even of small intensity (0.01 T), these liposomes become elongated in the direction of the field; the study of this deformation may be a way to measure the elasticity modulus of the membrane.