Abstract: To study the antioxidant system of Nelumbo nucifera seedlings in response to arsenic stress, compared the influence of two valences of inorganic arsenic, As (Ⅲ) and As (V), on soluble protein content, malondialdehyde(MDA)and the antioxidant system. Results showed that: MDA and soluble protein content of N. nucifera seedlings increased and then decreased with increasing concentration; MDA and protein content were more sensitive to As(Ⅲ)than to As(V)treatment. The Superoxide Dismutase(SOD)was the most sensitive to arsenic treatment; when the concentration of As (Ⅲ)was 2.5 μmol/L and As(V)was 100 μmol/L, the activity of SOD increased significantly. When the concentration of As(Ⅲ) was 10 μmol/L, the activity of Peroxidase(POD)increased significantly. The Catalase(CAT)was more sensitive to As(V). From the experimental results, with the increase in arsenic concentration, the enzyme activities of SOD, CAT and POD increased, which can be used to eliminate reactive oxygen species(ROS) and maintain cell metabolism stability. This study provides some basic data for further study of N. nucifera physiology and growth change, cultivation and transplants with arsenic stress.