Abstract: The membrane permeability, MDA contents, SOD and POD activities and cell ultrastructure of the oneyear seedlings of two Broussonetia papyrifera varieties under different NaCl treatments were studied. The results were as follows: (1)With an increase in NaCl stress and treating time, the membrane permeability and MDA contents in both cultivars increased considerably. The membrane permeability and MDA contents in the B.papyrifera cultivar increased more quickly thus suffered greater damage at higher NaCl concentrations. The activities of SOD and POD increased firstly and decreased later for both cultivars. The coordinated changes of activities among the antioxidant enzymes of SOD and POD could scavenge ROS and maintain a balance of ROS accumulation in cells to protect membrane structure. (2)The cell ultrastructure in leaves of two cultivars didn’t destroy under 0.1 % and 0.2 % NaCl and mitochondrial grew in number. With the increasing NaCl stress, the cell ultrastructure changed remarkably, the cellular organs for both cultivars became deformed and vacuole augmented under NaCl. Besides, the nucleolus diminished obviously and nucleolus matter agglomerated and the mitochondria structure was indistinct. Altogether, we concluded the B.kazinoki cultivar had greater salttolerance.