Abstract: The effects of manganese contamination on various enzymatic and non-enzymatic antioxidants in the leaves of Polygonum lapathifolium Linn. were studied. As a newly identified manganese hyperaccumulator, P.lapathifolium was grown in soils with various Mn concentrations for 70 d. Plant leaves were analyzed for activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and contents of ascorbic acid (AsA), glutathione (GSH), phytochelatins (PCs), total acid soluble SH, malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and superoxide anion (O₂^·-) evolution rate. The results showed that Mn content in the roots, stems, and leaves of P. lapathifolium increased with Mn concentrations in the soil. Both the MDA and H₂O₂ contents significantly increased with Mn treatment. However, the biomass of P. lapathifolium showed no significant differences compared with that of the control. The activities of SOD, POD, APX and AsA significantly decreased with increasing Mn treatment, which indicated that P. lapathifolium stimulated the antioxidant enzyme system. The contents of GSH, PCs and -SH were significantly higher than those of the control. These results indicate that both enzymatic and non-enzymatic antioxidants play significant roles in Mn detoxification in this plant.