Fe81Ga19 alloy ribbons were prepared by melt-spinning. The phase structure and magnetostriction of ribbon samples were investigated by XRD and M-TG. The results show that the matrix of Fe81Ga19 ribbons was disordered Fe(Ga) solid solution, accompanied with a small amount of the second phase maintaining an unsymmetrical DO3 structure. The [100] preferred orientation was formed along the thickness direction. The maximum magnetostricton of –1830×10-6 was obtained when the magnetic field was applied normal to the ribbon plane. The shape anisotropy of ribbons, the unsymmetrical DO3 structure and the [100] preferred orientation are suggested to be responsible for the giant magnetostriction.