ulse legumes including bean, cicer and lentil together with sainfoin as a pature plant are commonly grown in large scale in western and central parts of Iran (Kermanshah, Lorestan, Isfahan and Chahar Mahal and Bakhtiari) as human food or livestock feed. Like other legumes, bean, cicer, lentil and sainfoin have the unique ability to form a symbiotic relationship with rhizobia which promotes legumes growth through nitrogen fixation . Rhizobia are soil bacteria and able to elicit nodules on the roots of their specific host leguminous plants in which they convert atmospheric nitrogen into forms usable by the host plant. It is believed that there is a considerable genetic diversity among soil populations of rhizobia which is important for selection of efficient inoculants strains. However population genetic structure of rhizobia are different in the distinct geographical areas and it is important to evaluate the abundance and diversity of rhizobia nodulating different hosts in various areas. The aim of this study was the estimation of diversity within bean, cicer, lentil and sainfoin nodule forming rhizobia collected from different soils in western and central part of Iran. These investigations consist of PCR-RFLP and determination of nucleotide sequence of 16S rDNA region in addition to tracking and sequencing of genes that directly effect on symbiosis. The results of molecular analysis of the rhizobial isolates from bea showed that Rhizobium etli bv. phaseoli is the predominant bean- nodulating species in in the province of Kermanshah, Lorestan, Isfahan, Chahar Mahal and Bakhtiari. The investigation of Sinorhizobium fredii and Rhizobium leguminosarum bv. viciae in association with beans revealed the diversity of rhizobia isolated from beans from different sites and illustrated the complexity of the bean nodulating bacteria in various soils of Iran. The results also indicated that lentile is exclusively nodulated by R. leguminosarum bv. viciae and based on molecular analysis, almost all the lentile nodulating strain are similar. The chickpea strains were found to belong to Mesorhizobium cicer , which were phenotypicaly distinct from a few isolates identified as Agrobacrium tumefaciens . The cluster analysis performed based on 16S ribosomal DNA, nifH and recA sequencing results. revealed a high degree of heteogeneity among sainfoin nodulating rhizobia. The majority of these rhizobia were belong to R. leguminosarum bv. viciae, although few strains were identified a R. giardinii . Based on colony morphology, growth rate and PCR-RFLP of 16S ribosomal DNA profiles results the remained sainfoin isolats were found related either to Mesorhizobium sp. or Bradyrhizobium sp. On the basis of