Abstract: The effect of low pH on growth of rhizobium of Pueraria lobata was studied in this paper. PR390 was studied in this trail and the effect of low pH on growth of PR390 was investigated. The results indicated that low pH obviously inhibited the thalli and colony of PR390. The lower the acidity was, the slower the growth of rhizobia with the characteristics of a longer lag phase, a lagged log phase, a delayed stationary phase and a longer generation time were. The number of rhizobia decreased with the pH value of soil reducing. Furthermore, the results indicated PR390 had strong acid-tolerant ability and showed resistance to low pH.