Abstract: Effects of simulated acid rain(SiAR) at pH 3.0 and 3.5, along with pH 5.6 (CK), on the membrane permeability of cells in leaves of Brothin tomato were investigated. The results showed that the SOD activity, malondialdehyde (MDA) content, and cell membrane permeability of the tomato leaves increased significantly after SiAR treatments. But, the soluble protein decreased significantly due to the treatments. SOD activity in the leaves declined gradually once the stress was stopped.It became significantly lower than that of control, 20ds after the cessation. MDA content in the leaves treated by pH3.5 SiAR fluctuated with a slight upward trend that was not significantly different from that of control. On the other hand, the pH3.0 treatment produced a significant difference between them after 20ds of removal of the stress. The pH 3.5 treatment caused an initial rise on the membrane permeability and follo wed by a decline, while pH3.0 gave a continual downward trend. However, 20ds after stress stopping, there were no significant differences on the permeability between either of them and control.The soluble protein content in the leaves had an up-and-down insignificant increasing tendency by SiAR treatments in 15 days after the treatment. The injuries on the leaves caused by SiAR declined following the treatments, and reached a constant level 10ds after the stress ceased. Judging by the appearance of the tomato plants, the leaf yellowing and withering persisted 20ds after cessation of the pH3.0 treatment, indicating that an irreversible damage had occurred to the plants by SiAR. In contrast, the tomato plants seemed capable of self-rejuvenation after a SiAR stress at pH3.5.