The superplastic deformation curves of Zn-5Al eutectic alloy containing small amount of rare earth were measured, and the influence of rare earth on structure and superplasticity characteristics of the alloy was examined with optical microscope, XDF and TEM. The results show that the elongation of Zn-5Al eutectic alloy can be increased if less than 0.2 %(mass fraction) misch-metal was added. Rare earth which exists in the form of compounds Al2CeZn2 and CeZn3 can refrain the dissolution and diffusion of Zn to Al and postpone the saturation of the diffusion-dissolution zone(DDZ) above 350 ℃, and in such a way boost up α/β interface sliding which benefits the superplasticity.