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The germination percentage and the ultrastructure of radical cells of Aesculus chinensis seeds which dehydrated for different days were studied in this paper. The result showed that the water content of mature A. chinensis seeds was high up to 1.46 g/g( DW). When water content was lower than 1.07 g/g(DW) , further desiccation would decrease the germination percentage of seed dramatically. The radical cell of mature A. chinensis seeds were fully differentiated, and all cell organelles were shown up completely and clearly. The nucleus were large and situated in the middle of the cell. The nuclei membrane as well as the crista and outer membrane of mitochondrion were clear. The endoplasmic reticulum and golgi apparatus could be seen clearly, and the vacuoles were small. However, endoplasmic reticulum in the form of annulated lamellar structure was observed in cells after they were desiccated for 5 days and it became more and larger after desiccation for 7 days. The autophagic vacuoles in embryonic cell were observed after desiccation for 7 days. The annulated lamellar structure was not repaired after backwater. It is corresponding to the sharp decrease of seed germination percentage.