To characterize differences in soybean resistance to salt stress, two soybean species, the wild salt-tolerant soybean Glycine cyrtoloba(serial number ACC547) and the cultivated salt-sensitive soybean G. max(cv. Melrose) were treated with 0, 50, 100, or 150 mmol L-1Na Cl for 5 days. A series of physiological parameters were determined in both shoots and roots, including content of chlorophyll(Chl) and malondialdehyde(MDA); electrolyte leakage(EL); hydrogen peroxide(H2O2) concentration; superoxide oxygen radical(O2-)production rate; activities of several enzymes including superoxide dismutase(SOD),catalase(CAT), and peroxidase(POD); and selective ion(Na+and K+) accumulation. Our results showed that the relative salt tolerance of ACC547 was associated with lower loss of Chl content; lower MDA content, EL, H2O2 concentration, and O2-production rate in both shoots and roots; higher POD activity caused by new isoforms in roots; and higher K+concentration and K+/Na+ratio in shoots. These results suggested that relative lower membrane injury, efficient K+vs. Na+selective accumulation, and newly induced POD isoenzymes are mechanisms of salt tolerance in soybean. To characterize differences in soybean resistance to salt stress, two soybean species, the wild salt-tolerant soybean Glycine cyrtoloba (serial number ACC547) and the cultivated salt-sensitive soybean G. max (cv. Melrose) were treated with 0, 50, 100 , or 150 mmol L -1 NaCl for 5 days. A series of physiological parameters were determined in both shoots and roots, including content of chlorophyll (Chl) and malondialdehyde (MDA); electrolyte leakage (EL); hydrogen peroxide ; activities of several enzymes including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD); and selective ion (Na + and K +) accumulation. Our results showed that the relative salt tolerance of ACC547 was associated with lower loss of Chl content; lower MDA content, EL, H2O2 concentration, and O2-production rate in both shoots and roots; higher POD activity caused by new isoforms in roots; and higher K + concentration and K + / Na + ratio in shoots. These resu lts suggested that relative lower membrane injury, efficient K + vs. accumulation and newly induced POD isoenzymes are mechanisms of salt tolerance in soybean.