Abstract: We observed the ultra structural changes of mesophyll cells in flue-cured tobacco leaves under NaCl stress by TEM, and analyzed the response of cell structure with NaCl stress. The results showed that the chloroplasts were morphologically integrated before NaCl treatment, and no evident morphology changes existed with the increased treatment time, with well-preserved mitochondrial envelope, high concentration of karyolymph, clear structure of vacuole, and tight link between cytoplasm and cytoderm. While under NaCl treatment, the thylakoid of chloroplast appeared swelling and rupturing, and morphologically broken down, and the grana lamella became incompact, deformed, fractured and completely disorganized. The treated mesophyll cell exhibited no apparent rupture of envelope, and the inner membrane of mitochondrial became invaginated and fractured, yet the outer membrane was partially damaged. The karyolymph exhibited lower concentration and apparent heterochromatinization. The nuclear membrane degraded partly and became ambiguous, and the proportion of vacuole was smaller with plasmolysis.