Gene BADH was transformed into alfalfa (Medicago sativa L.) through Agrobacterium-mediated transformation method, and salt tolerance of the transgenic progenies was assessed. Among 247 plants obtained after transformation, 43 were positive by polymerase chain reaction (PCR) detection using the primers specific for BADH gene. Reverse transcription polymerase chain reaction (RT-PCR) analysis indicated that gene BADH was expressed in 42 plants at transcriptional level. Southern blotting analysis also showed that the target was integrated into Medicago genome. The transgenic plants grew vigorous in salt stress condition, whereas the wild type plants was retarded and did not survive after cradle. The relative electrical conductivity and malondialdehyde (MDA) contents in the T(1) transgenic plants were lower, but peroxidase (POD) and superoxide dismutase (SOD) activities were higher than those of the wild type plants. These results demonstrated that the expression of foreign BADH gene enhanced the salt tolerance in transgenic alfalfa.