This study investigates arsenic (As) accumulation and tolerance of duckweed Spirodela polyrhiza L. and its potential for As phytofiltration. S. polyrhiza was able to survive in high concentration of As(V) solution. The EC50 values (± SE) based on the external As(V) were (181.66 ± 20.12) μmol/L. It accumulated (999 + 95) mg As/kg dw when exposed in 320 μmol/L As(V) solution for one week, and was able to take up appropriately 400 mg As/kg dw in tissues without a significant biomass loss. The EC50 values (the effective concentration of As(V) in the nutrient solution that caused a 50% inhibition on biomass production) was (866 + 68) mg/kg dw for the tissues, indicating that S. polyrhiza had a high capability of As accumulation and tolerance. The uptake kinetic parameters Vmax was (55.33 + 2.24) nmol/(g dw.min) and Km was (0.144 + 0.011) mmol/L. Within 72 hr, S. polyrhiza decreased As concentration in the solution from 190 to 113 ng/mL with a removal rate of 41%. The study suggested that this floating aquatic plant has some potential for As phytofiltration in contaminated water bodies or paddy soils.