Alterations in physiological and biochemical responses under arsenic (As) phytotoxicity were investigated in aquatic model plant, Spirodela polyrhiza L. Decrease in dry matter and total chlorophyll was observed in this plant under treatment at increasing concentrations. Similar decrease in protein and carotenoid contents was also recorded compared to the control. Increase in malondialdehyde, an index of lipid peroxidation, membrane damage and ion leakage increased under As treatment as compared to the non-treated plants. Accumulation of As was found to be maximum at higher concentration as compared to the control samples. This study revealed that As imposed stress increased the membrane damage, as is evident by the increased values of electrical conductivity and lipid peroxidation under repeated exposure.