The toxicity symptoms, changes of leaf morphological structures and chloroplast ultrastructures of Phytolacca americana under manganese stress were investigated using hydroponic culture with different concentrations of manganese (Mn). The results indicated that this Mn hyperaccumualator species has a remarkable tolerance to Mn. Under nutrient culture conditions, P. americana could grow quite well with Mn supplied at a concentration of 1000 μmol/L. With the increase of Mn concentration in the culture solution, the leaf morphological structures and chloroplast ultrastructures of P. americana had some changes. At the Mn concentration reached 5000 μmol/L, the leaves showed chlorosis and injury symptoms with yellow-brown spots on the leaf surface. When Mn concentration exceeded 12000 μmol/L, the leaves showed purple spots on the surface during the 30-day Mn exposure, with an injury rate of 87.33%. Significant changes in leaf structure were noted, with swollen palisade cells which arranged loosely. When Mn concentration reached above 12000 μmol /L, the mesophyll and epidermal cells were distorted. With further increase of Mn concentration, the chloroplasts were shrunk with outer membrane disrupted, and the thylakoids swollen and became heavily hollowed. The stroma lamellae was distorted and grana disordered or blurred as floc, starch grains became smaller and less, and osmiophilic granules increased. Although the leaf morphological structures and chloroplast ultrastructures of P. americana had significant changes under heavy Mn stress, this species could still survive and grow. All these suggested that P. americana had an extraordinary tolerance to Mn.