Abstract: In order to discover acid-tolerant Rhizobium meliloti that can nodulate alfalfa high-effectively on acidic soil, researches were explored to isolate rhizobia from alfalfa nodules on acidic soil (pH5.2), methods based on the thesis of adaptive acid-tolerance response of the Rhizobia were adopted, six strains were isolated, which could grow on solid medium with pH4.8 steadily. In addition, the nodulation characteristics, growth curves and mean generation time under different acidity of the strains were examined. The results showed that all the rhizobia could nodulate alfalfa with enough nodules (≥10) and high nodulation ratio (about 66.67%~100%); under different acidity, the rhizobia represented different growth characteristics, acid slowed strains’ growth rate significantly, which made the rhizobia exhibit a prolonged lag phase, a lagged log phase and a delayed stationary phase, the mean generation time under acidic condition was longer than that under neutral condition, the lower the pH was, much longer the mean generation time was. However, the acid-tolerant rhizobia, if exposed to the tolerant acidity range, could still grow quickly after a prolonged lag phase