Abstract: The GsGST13 gene was selected based on the Glycine soja gene transcriptome of salt-alkaline stress. The high-sulfur-containing amino acids gene SCMRP was designed using the bioinformatics codes. The plant binary expression vector (pBEOGST13/SCMRP) was designed and transferred into alfalfa (Medicago sativa cv. Nongjing No.1) using the Agrobacterium-mediated method. Many over-expression transgenic alfalfa lines were obtained, and two of them were selected to analyse the salt resistance and sulfur amino acids contents. Transgenic alfalfa lines showed enhanced tolerance to NaCl stress compared with wild-type plants. Under NaCl stress, the growth of wild-type plants was inhibited, the blade gradually became yellow and crimp panama, but there was only a slight effect on the transgenic lines, which had normal growth under stress. The malondialdehyde and hydrogen peroxide contents of transgenic lines were significantly lower than those of non-transgenic lines (P<0.05). Moreover, plant height, fresh weight, GST activity and SOD activity of transgenic alfalfa were significantly (P<0.05, P<0.01 respectively) higher than those of non-transgenic lines under salt stress conditions. Further, the sulfur amino acids contents of the G₁₆ and G₅₀ transgenic alfalfa lines were higher than those of wild type plants, by 0.57% and 0.52%, respectively. Over-expression of the GST13 and SCMRP in alfalfa improved the tolerance to salinity stress and increased the content of sulfur amino acids.