The increased concentrations of lead (Pb) are found to be highly toxic to soil microorganisms and can affect their structural diversity. Therefore, the present study aimed to induce superior strains of the bacterium Rhizobium by EMS mutagenesis of wild-type RL16 andexamined the effects of developed mutants on the crop yield of pea plants in the experimental greenhouse. Nine superior mutants of Rhizobium were developed to tolerate the wild-type strain's LC95 concentration (6.3 mM Pb (No3) 2). This study demonstrated that the mutants could produce more extracellular proline than the wild-type, increasing their ability to survive in lead heavy metal stress conditions. Rhizobium application improves the pea characters and Rhizobium mutants indicate better recovery because the mutants were more tolerant to Pb than the wild-type strain.  Also, the results demonstrated that Rhizobium mutants' inoculation showed more proline production by pea plants which agrees with their ability to recover the negative effect of Pb contamination in pea characters. PCR amplification of the pbrA gene showed that all wild-type and mutants contained the Pb-resistant gene.