The ultradry preservation of the rare and endangered species Populus euphratica seeds was carried out to determine the optimal moisture content and rewetting method in this paper. The feasibility of ultradry preservation of P. euphratica seeds was determined by measurements of contents of various enzymes, soluble sugar and malondialdehyde(MDA). The P. euphratica seeds with different water contents were prepared by the method of dehydration of silica gel. The seeds were rewetted with different solutions, and the optimal wetting method was selected. After treated by aging, the activities of enzymes, soluble sugar, and malondialdehyde in the optimum moisture content of seeds were determined after rewetting to determine the effect of ultradry preservation. The results showed that: (1) the seed germination rate decreased with the water content decreased to 3.4%. The seed germination rate and germination potential of P. euphratica seeds could be restored to the samples without ultradry treatment after rewetting. The optimum moisture content was determined as 3.4%. (2) After comparison of four different methods, the results showed that rewetting with saturated NH₄Cl for 12 h after rewetting with saturated CaCl₂ was a better method of rewetting. (3) The aging results showed that the suitable ultradry treatment could increase the activities of peroxidase, catalase, dehydrogenase and the content of soluble sugar, and decrease the content of MDA in the seeds with 3.4% moisture at 50 ℃. Therefore, ultradry preservation of P.euphratica seeds has a certain feasibility for enhancing the antiaging ability of the seeds.