Abstract: The ultrastructural changes of root cells of Fraxinus americana and Prunus maritima under different salt stresses (CK, 3 g/L, 9 g/L) for four months were studied by applying transmission electron microscopy.The results showed that the cytoplasm of root cells of Fraxinus americana agglomerated, and the plasmolysis was obvious, organelles were seriously degraded under lowsalt stress (3 g/L), The nuclear membrane was partially dissociated from the nuclear, but the root cell wall structure of F.americana was basically normal.While there were no significant changes to root cells of Prunus maritima.Under highsalt stress (9 g/L), root cells of Fraxinus americana were severely damaged, plasmolysis was further developed.While there were more degraded materials accumulated in the root cells of Prunu maritima, and the organelles were degraded under high salt stress.The concentration of nuclear chromatin declined and the nuclear membrane became fuzzy.The cytoplasmic membrane was partially invaginated but there was no obvious plasmolysis observed in the root cells of P.maritima.In comparison, root cells of Fraxinus americana were more seriously damaged under salt stress and Prunus maritima exhibited to be more resistant to salt stress.