Abstract: To understand whether nodulation affects salt stress response in alfalfa (Medicago sativa), we analyzed the content of methane dicarboxylic aldehyde (MDA), superoxide anion radical, activity of superoxide dismutase (SOD), glutathione (GSH), proline, and soluble sugar in alfalfa under salt stress. Four-month-old alfalfa plants without nodules, with active nodules, or with inactive nodules were treated for 0, 5, 10 and 15 days. Alfalfa plants with nodules, especially with active nodules, had less MDA. The MDA contents of roots, stems, and leaves reached a low point, of 3.90, 0.53, 4.16 mmol/g DW respectively at the 15th day. The least superoxide anion radical and the SOD activities of roots, stems, and leaves were highest in the 15th day with activities of 1 592.48, 1 317.86, 2 068.88 U/g DW·h, respectively and with stable GSH, but unstable content of proline and soluble sugar. The results suggested that alfalfa with active nodules may have higher osmoregulatory and antioxidative capability under salt stress.