Abstract: To study the effects of inorganic trivalent arsenic stress on Ludwigia peploides (Kunth) P. H. Raven subsp. stipulacea (Ohwi) P. H. Raven, sterile immature plant of Jussiaea stipulacea Ohwi cultured in 1/2 Hoagland nutrition liquid with NaAsO₂ at 0, 2.5, 10, 50, 250, 500 μmol/L respectively for 24h were analyzed the photosynthetic system and physiological and biochemical characteristics by measuring the contents of chlorophyll, malondialdehyde (MDA), soluble protein, soluble sugar and activity of antioxidant enzymes (SOD, POD, CAT). Results revealed that the chlorophyll a, b, and a+b contents reached their peaks at 2.5 μmol/L As (Ⅲ), but the chlorophyll contents decreased gradually with the increased As (Ⅲ) concentration. As (Ⅲ) induced MDA content with the highest level at 500 μmol/L that was significantly higher than that in the control group. The soluble protein content first increased and then decreased with the increased As (Ⅲ). The soluble protein content was significantly higher at 250 μmol/L group than that of the control group, and it was lower at 500 μmol/L group than the control group. The soluble sugar content firstly decreased and then increased with the increase of arsenic concentration. Activity of antioxidant enzymes (SOD, POD and CAT) increased gradually at low As (Ⅲ) concentration to reach significant difference, but they decreased when the As (Ⅲ) concentration was higher than 250 μmol/L, suggesting that under low As (Ⅲ) concentration, Jussiaea stipulacea Ohwi itself will appear self-protection, and high As (Ⅲ) concentration will have damage effect. The results provide a basis for further study of Jussiaea stipulacea Ohwi physiology and growth change, cultivation and transplants with arsenic stress.