Mercury (Hg) content as well as its effects on growth and antioxidative metabolism were investigated in the seedlings of Sesbania drummondii, cultivated on different concentrations of Hg (0-100 ppm). Hg concentration in shoot as well in root increased with increasing Hg concentrations in the growth medium. Accumulation of Hg in root was higher than shoot. At 100 ppm Hg concentration, shoot accumulated 1,911 mg Hg/kg of their dry weight (dw) while root accumulated 62,166 Hg/kg dw. Scanning Electron Microscopy of treated tissue also confirms the presence of Hg metal in different parts of plant. At lower concentrations of Hg, plants growth was not significantly affected; however, at higher concentrations growth was affected significantly. A concentration of 100 ppm Hg inhibited growth by 36.8%, with respect to control. Photosynthetic activity was assessed by measuring chlorophyll a fluorescence by determination of Fv/Fm and Fv/Fo values. Photosynthetic integrity was affected when plants were grown at Hg concentration of >50 ppm. S. drummondii plants responded to Hg induced oxidative stress by modulating non-enzymatic antioxidants (glutathione, other non-protein thiols) and enzymatic antioxidants: superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR). The content of glutathione (GSH) and GSH/GSSG ratio increased up to a concentration of 50 ppm and decreased at 100 ppm Hg. The content of other non-protein thiols significantly increased with increasing Hg concentrations in the growth medium. The activities of SOD, APX and GR also increased up to a concentration of 50 ppm Hg and then decreased at higher concentration. The results suggest that Sesbania plants were able to tolerate Hg induced stress using an effective antioxidative defense mechanism.