Vallisneria natans (Lour.) Hara, a widely distributed submerged aquatic plant, is a promising species for arsenic (As) removal from contaminated water. We investigated the effects of pH on the accumulation, subcellular distribution and detoxification of As in V. natans. The results showed that the optimum pH for submerged V. natans growth is close to 7.0. The accumulation of As in the plant increased with the increase of pH (p < 0.05). This may have been due to arsenic/phosphate transporters with a higher affinity for the more highly electronegative AsO4 (3-) than for HAsO4 (2-) and H2AsO4 (-). After As(V) was accumulated by plants, more than 80 % was reduced to As(III), but As reduction decreased with increased pH. The majority of accumulated As and reduced As(III) (47 %-66 %) was found in the vacuoles. Higher As concentrations in vacuoles could be considered as an important mechanism for As detoxification in submerged plants.